# Siren

> Siren is a notification infrastructure platform that routes messages from an application or an AI agent across email, SMS, WhatsApp, push, in-app, Slack, Microsoft Teams, Discord, and LINE through one API, using a visual workflow builder, multi-channel templates, provider pools that fail over between vendors, and an agent toolkit and MCP server that let a model trigger those workflows directly.

- Category: Notification Infrastructure (https://saastracker.org/categories/notification-infrastructure)
- Website: https://trysiren.io
- Starting price: $249 per month, or $208 per month billed annually
- Free plan: No
- Free trial: 7 days with everything unlocked, no credit card required
- Founded: 2024, HQ: Kochi, Kerala, India, Ownership: Bootstrapped. Built and operated by KeyValue Software Systems Private Limited, a product engineering studio running since 2017.
- Profile last reviewed: 2026-09-13
- Canonical profile: https://saastracker.org/products/siren

## Key facts

| Attribute | Value | Source |
| --- | --- | --- |
| Free tier volume | None; 7-day full-feature trial only | trysiren.io/pricing, checked 2026-09-13 |
| First paid tier | $249 per month, or $208 per month billed annually (Pro) | trysiren.io/pricing, checked 2026-09-13 |
| Paid tier volume | 100,000 notifications per month on Pro | trysiren.io/pricing, checked 2026-09-13 |
| Self-hosting | Not offered; managed cloud only | docs.trysiren.io, checked 2026-09-13 |

## Overview

Every platform in this category assumes a backend service decides when a person gets told something. Siren assumes the decider might be a model. The product carries the usual notification infrastructure apparatus (workflows, templates, provider routing, an in-app inbox, delivery logs) and then adds the surfaces an agent needs: an MCP server, a function-calling toolkit for OpenAI, LangChain, and Vercel agents, and a chat node that posts an interactive message into Slack, Teams, or Gmail with buttons and waits for a human to answer inside the running workflow. If your roadmap includes an agent that has to ask someone for approval before it acts, that last piece is the reason to look here.

Siren is built and operated by KeyValue Software Systems Private Limited, a bootstrapped product engineering studio in Kochi, Kerala that has been running since 2017. The product first appeared publicly in 2024. There is no disclosed venture funding behind Siren itself, which cuts both ways for a buyer: no investor clock forcing a pivot, but also no funding announcement, no published customer count, and a smaller public track record than the venture-backed names in this category. Treat it as a capable young product from an established services company rather than as a startup with a war chest.

Channel and client breadth is where Siren is genuinely ahead of its better-known rivals. Nine channels ship out of the box, including WhatsApp, Discord, and LINE, which matter for products with users in Asia and in communities. On the front end, the inbox has SDKs for JavaScript, React, Vue, React Native, Android, and Flutter, so a team not building in React gets a supported component instead of a REST API and a weekend. Delivery runs through your own provider accounts (SendGrid, Amazon SES, Postmark, Mailgun, Gmail, Outlook, Loops, Twilio, Plivo, MSG91, Kaleyra, MessageBird, Meta WhatsApp, Gupshup, WATI, Firebase, OneSignal), and provider pools let you group several accounts of the same channel with message limits so traffic rolls to the next vendor when one is exhausted or down.

Pricing is the sharpest thing about it, in both directions. There is no free tier at all, which is unusual here: every direct competitor gives away between 1,000 and 10,000 notifications a month forever. Siren gives seven days with everything unlocked and then asks $249 a month, or $208 a month on annual billing. What that buys is 100,000 notifications, twice the volume Knock and MagicBell include at the same price, plus campaigns, cohorts, and unlimited workflows and templates. The caps to read before signing are 500 stored users, 30 campaigns, four team members, and 30 days of log retention.

## How it works

1. Recipients reach Siren one of two ways. You can store them as users through the API or the dashboard, with contact details per channel, language, a VIP flag, custom fields, and channel preferences, which is what campaigns and cohorts run against. Or you can leave them out of the platform entirely and pass the recipient inline in the trigger payload, which is how most event-driven product notifications work and which sidesteps the stored-user cap.

2. You author templates per channel in the dashboard, with variables, previews, and an AI assistant that drafts a first version, then version and publish them. Workflows are assembled visually from nodes: a template node picks the content, a channel node picks where it goes, a wait node pauses, control nodes branch on payload or user data, an HTTP node calls out to your own systems mid-flow, and a chat node posts an interactive message and holds the execution open for a reply. Publishing a workflow makes it callable.

3. Your application triggers a published workflow by posting to the trigger endpoint with the workflow name, a data payload, and recipient details, and a bulk endpoint does the same for batches. The same workflow can be fired from a server SDK in Python or TypeScript, from the MCP server as a tool call, or from the agent toolkit as a function an LLM chooses to call. Every trigger returns a request id and a workflow execution id you can trace.

4. Delivery uses your own provider credentials, so you keep your sending reputation and your negotiated rates. Three workspaces (Sandbox, Staging, and Production) hold their own templates, providers, and keys so a test send cannot reach a customer. Logs record a per-channel lifecycle (submitted, delivered, read or opened, clicked, with the honest caveat that Slack, Teams, and Discord report submission only) and export to CSV. Webhooks push delivery events back to you, signed with a signature header, and the public API is rate limited to 60 requests a minute by default.

## Best for

Product and platform teams shipping multi-channel notifications where an AI agent is one of the senders, where the audience lives on WhatsApp, LINE, or Discord as well as email, or where the in-app inbox has to render in Vue, Flutter, or native Android rather than React.

## Not the right fit for

- Teams that need a free production tier; there is none, so after seven days the decision is $249 a month or nothing, and every direct competitor lets you run small workloads free forever.
- Consumer products with large stored audiences; Pro allows 500 users in the platform, and while event-triggered sends can pass recipients inline, campaigns and cohorts cannot exceed that cap.
- Teams whose core requirement is digests; Siren has waits and branching but no batching or digest primitive, which is the single feature most buyers come to this category for.
- Marketing teams without engineering; workflows are no-code once they exist, but nothing fires until your application, an SDK, or an agent calls the trigger endpoint.
- Buyers who need a compliance pack in the evaluation; Siren publishes no SOC 2, ISO 27001, or HIPAA attestation, so a security review that requires one will stall.

## Features

### Workflow orchestration

A visual builder that decides what gets sent, where, and what happens while it waits.

- **Node-based visual builder**: Workflows are assembled by clicking nodes together rather than by writing orchestration code, then published as a named, callable unit your backend triggers by name.
- **Template and channel nodes**: One node chooses the content, another chooses the channel, so the same message can fan out or fall back without duplicating the template.
- **Wait nodes**: Pause a workflow for a fixed period before the next step, which is how reminders, escalations, and second-touch sequences get built.
- **Control nodes for branching**: Route on payload values or user attributes so one workflow serves several segments, tiers, or regions instead of being copied five times.
- **HTTP nodes**: Call your own API from inside a running workflow, check a condition, and continue on the answer, which keeps state lookups out of the triggering service.
- **Chat node for human replies**: Posts an interactive message with buttons into Slack, Microsoft Teams, or Gmail, keeps the thread id, and holds the workflow execution open until a person answers. Currently in beta.
- **Single and bulk triggers**: One endpoint fires a workflow for a recipient, another fires it for a batch, both returning an execution id you can trace in the logs.
- **Test and trigger in the editor**: Run a workflow against sample data from inside the builder before publishing, so the first real trigger is not the first execution.

### Channels and providers

Nine channels, your own vendor accounts, and failover between them.

- **Nine delivery channels**: Email, SMS, WhatsApp, push, in-app, Slack, Microsoft Teams, Discord, and LINE, each with its own template editor rather than one template stretched across all of them.
- **Bring your own provider accounts**: Email through SendGrid, Amazon SES, Postmark, Mailgun, Mailchimp, Gmail, Outlook, or Loops; SMS through Twilio, Plivo, MSG91, Kaleyra, or MessageBird; WhatsApp through Meta, Twilio, Gupshup, MSG91, or WATI; push through Firebase or OneSignal.
- **Provider pools**: Group several accounts on the same channel with per-provider message limits and time windows, and traffic moves to the next account when one hits its limit or fails, which is real vendor redundancy rather than a single configured sender.
- **Default provider per channel**: Set which account a channel uses when a workflow does not name one, so adding a second vendor does not require editing every workflow.
- **Cross-channel templates**: Design, preview, and test one message across the channels it will appear on, with variables shared between them and versions published deliberately.
- **AI template drafting**: An assistant writes a first version of a channel template from a prompt, which removes the worst hour of any notification project even when the draft gets rewritten.

### Agent and AI surface

The part that separates Siren from the rest of the category.

- **MCP server**: Exposes sending, templates, users, and workflow triggers as Model Context Protocol tools, with documented setups for Claude Desktop, Cursor, VS Code, Amazon Q CLI, and any other MCP client.
- **Agent toolkit**: Function-calling tools for OpenAI, LangChain, and Vercel agents in Python and TypeScript, so an agent can choose to notify a person as one of its available actions.
- **Human in the loop workflows**: The chat node plus a message replies API turns an approval, an escalation, or a clarifying question into a step the agent waits on rather than a dead end it has to guess past.
- **Prebuilt agent templates**: A library of production-ready patterns for agent-specific cases such as approval flows and error escalations, importable and editable rather than written from a blank page.
- **QuickSend**: Sends a single notification without defining a workflow first, which is how most integrations get their first message out inside an afternoon.

### Users, cohorts, and campaigns

The list-driven half, which most pure infrastructure platforms in this category do not have.

- **User records with channel preferences**: Store contact details per channel, language, country, VIP status, and custom fields, and set which channels a given user accepts.
- **Inline recipients on trigger**: Event-driven sends can pass the recipient in the trigger payload instead of storing them, which matters because stored users are capped on the published plan.
- **Cohorts and segments**: Build audiences from stored user attributes and use them for bulk actions and campaign targeting, with no limit on the number of cohorts on either paid plan.
- **Campaigns with scheduling**: One-time, recurring, and event-tied sends against a cohort, scheduled and monitored from the dashboard, with 30 campaigns included on Pro.
- **Data source connections**: Connect PostgreSQL or Mixpanel to define the target audience from data you already keep, rather than maintaining a second copy of it inside the notification tool.

### Operations and observability

What you have to live with after the integration ships.

- **Three isolated workspaces**: Sandbox, Staging, and Production each carry their own templates, providers, and API keys, so promoting a change is deliberate and a test send cannot reach a customer.
- **Per-channel delivery lifecycle**: Logs record submitted, delivered, read or opened, and clicked, with honest gaps documented: Slack, Teams, and Discord report submission only, and WhatsApp read receipts depend on the recipient's settings.
- **CSV log export**: Filter the log view and export it, which is how most teams get notification data into a warehouse without an integration project.
- **Signed webhooks**: Delivery events post back to your endpoint with a signature header to verify origin and a delivery header to deduplicate retries.
- **Published API rate limit**: 60 requests a minute by default, with limit, remaining, and reset values returned in response headers, which is a specific number more vendors should publish.
- **Dashboard analytics**: Channel and workflow level delivery reporting in the console, with 30 days of log retention on Pro and contract-defined retention on Enterprise.
- **Role and permission controls**: Team member roles and permissions are configurable, with four members included on Pro and member access negotiated on Enterprise.

## Use cases

- **Team shipping an AI agent that has to ask permission**: The agent can draft the refund, the discount, or the outbound reply, but a human has to approve it, and the approval currently lives in a Slack message somebody wrote a bot for. Outcome: A chat node posts the request with approve and reject buttons, the workflow execution waits, and the agent resumes on the answer, so the approval is a step in the flow rather than a separate integration.
- **B2B product with users across Asia**: Customers read WhatsApp and LINE, not email, and the incumbent notification platform covers neither without a custom provider integration. Outcome: Both are first-class channels with their own templates and provider choices, so the same workflow reaches a Gmail user and a LINE user without a branch in application code.
- **Platform team that lost a night to one SMS vendor**: A single provider outage stopped every verification code in the product, and the fallback plan was a deploy. Outcome: A provider pool holds two or three accounts per channel with message limits, and traffic rolls to the next one automatically, so the outage becomes a line in a log rather than an incident.
- **Product not built in React**: The requirement is an in-app notification inbox, and the leading platforms ship polished components for React and leave Vue, Flutter, and Android teams to build their own. Outcome: Siren ships supported SDKs for JavaScript, React, Vue, React Native, Android, and Flutter, so the inbox is an integration rather than a project.

## Pricing

A single published subscription priced on notification volume, with hard caps on stored users, campaigns, team members, and log retention, sold above a seven-day full-feature trial. No permanent free tier.

- **Free trial**: $0 for 7 days. Everything unlocked for seven days; All providers and channels; Full workflows, campaigns, and templates; Analytics, reports, roles, and permissions; API and webhooks enabled. A trial rather than a free plan. Nothing continues at $0 once the week is up.
- **Pro**: $249 per month, or $208 per month billed annually. Up to 100,000 notifications a month; Access to all providers and unlimited data sources; Up to 500 stored users, unlimited cohorts; Unlimited workflows and templates, 30 campaigns; 30 days of logs, API and webhooks, 4 team members. Twice the included volume of Knock Starter or MagicBell Startup at effectively the same price, with the stored-user cap as the trade.
- **Enterprise**: Custom volume-based contract. Volume-based pricing with custom provider additions; User count, cohorts, workflows, and campaigns scaled on request; Templates, notification volume, and log retention set per contract; Configurable member access; 24 by 7 enterprise support.

Billing notes:

- There is no permanent free tier, which is the structural difference from every other platform in this category; Knock, Novu, Courier, SuprSend, and MagicBell all give away volume forever.
- Annual billing is two months free, which takes the effective rate to $208 a month and saves $489 over a year.
- The published page states the 100,000 notification allowance but no overage rate, so confirm what a spike month costs before you plan capacity around it.
- 500 stored users is the binding constraint for anything consumer-scale, though event-triggered sends can carry the recipient in the payload rather than storing them.
- Delivery is billed by your own providers on top. Twilio, SendGrid, Meta, and the rest invoice you directly, so the Siren line is the orchestration layer only.
- Log retention is 30 days on Pro. Teams that need longer history for audit or support should export to CSV on a schedule or price the Enterprise contract.

Value assessment: On raw allowance Siren is the best value at its price point in this category: 100,000 notifications, unlimited workflows and templates, cohorts, campaigns, and nine channels for $249 a month, against 50,000 messages for $250 at Knock and 50,000 deliveries for $249 at MagicBell. The catch is the shape of the plan rather than the number. No free tier means you cannot prove the thing in production before paying, 500 stored users rules out consumer audiences on the published plan, and 30 days of logs is short for anything audited. For a small B2B product sending tens of thousands of notifications a month across several channels, this is the most capability per dollar on offer. For a team that wants to start at zero and grow into a bill, it is the wrong door.

## Strengths

- Nine channels out of the box including WhatsApp, Discord, and LINE, which is broader than any other platform in this category at a published price.
- In-app inbox SDKs for JavaScript, React, Vue, React Native, Android, and Flutter, so teams outside the React default get a supported component rather than a REST endpoint.
- Provider pools give genuine vendor redundancy with per-provider message limits and automatic rollover, which most rivals leave as a single configured sender per channel.
- The agent surface is real and specific: an MCP server, function-calling toolkits for OpenAI, LangChain, and Vercel, and a chat node that holds a workflow open while a human answers in Slack, Teams, or Gmail.
- Campaigns, cohorts, and data source connections to PostgreSQL and Mixpanel are included, so the list-driven half of notification work does not need a second tool.
- Sandbox, Staging, and Production workspaces ship on every plan, each with its own templates, providers, and keys.
- 100,000 notifications on the published plan is double what the two closest-priced competitors include.

## Limitations

- No free plan at all. Seven days of trial, then $249 a month, which is the hardest entry in the category and rules out hobby projects and long evaluations.
- No batching or digest primitive anywhere in the product or the documentation, and collapsing nine events into one notification is the single most common reason teams buy a platform like this.
- 500 stored users on the published plan, with campaigns and cohorts bounded by it, so consumer-scale list work needs an Enterprise conversation immediately.
- No published compliance attestations. There is no SOC 2 report, ISO certification, or HIPAA statement in the public documentation, which will stall procurement at any regulated buyer.
- Four team members and 30 campaigns on Pro are caps that a growing team will meet, and the page gives no per-seat or per-campaign price to grow past them.
- The chat node, which is the most distinctive feature, is still marked beta.
- Documentation is complete but thinner and less polished than Knock's or Novu's, and the public record on customers, scale, and reliability commitments is close to empty.
- Operated by a services studio rather than a funded product company, which means no disclosed runway, no public roadmap cadence, and a smaller support organisation behind a critical path system.

## Comparisons

- **Siren vs Knock**: The same job with opposite entry terms. Knock gives away 10,000 messages a month forever and charges $250 for 50,000; Siren gives seven days and charges $249 for 100,000. Knock is deeper where it matters to a B2B SaaS platform team: batching and digests, multi-tenancy, workflows as code in version control, environments, and documentation that is the best in the category. Siren answers with twice the volume, nine channels against Knock's six, inbox SDKs beyond React, provider pools, and an agent surface built for human-in-the-loop approvals. Take Knock if digests and tenant configuration are the problem. Take Siren if channel breadth, non-React clients, or agent-triggered notifications are.
- **Siren vs Courier**: Courier meters purely per send at $0.005 with 10,000 free a month, so a team sending 40,000 notifications pays about $150 and one sending 5,000 pays nothing. Siren is a flat $249 for 100,000, which only wins above roughly 60,000 notifications a month. Courier has the better template designer and the gentler on-ramp; Siren has WhatsApp, Discord, and LINE, provider pools, campaigns, and the agent toolkit. Below 50,000 notifications a month Courier is cheaper and easier. Above it, Siren buys more product for the money.
- **Siren vs Novu**: Novu is the open-source option: self-host the core for infrastructure cost only, or take the cloud from about $30 a month, with digests and an inbox component that Siren cannot match on digests at all. Siren is closed source, starts at $249, and offers more channels, more front-end SDKs, provider pools, and an agent toolkit. If self-hosting, data residency, or a small budget is the constraint, Novu is the answer and it is not close. If the requirement is WhatsApp and LINE delivery with vendor failover and an MCP server, Novu will not get you there.
- **Siren vs MagicBell**: Nearly identical price points with different centres of gravity. MagicBell is inbox-first, with a free Builder plan at 1,000 deliveries and a polished embeddable notification centre, then $249 a month for 50,000 deliveries. Siren is orchestration-first at $249 for 100,000 notifications, with the inbox as one channel among nine. Choose MagicBell when a refined in-app feed shipped quickly is the whole requirement and you want to start free. Choose Siren when the feed is one surface in a multi-channel program, especially on Vue, Flutter, or Android where MagicBell's component coverage thins out.
- **Siren vs SuprSend**: The closest match on ambition. Both carry orchestration, an inbox, preferences, WhatsApp, and Microsoft Teams, and both come from India-based teams shipping quickly. SuprSend starts free at 10,000 notifications a month and its first paid tier is around $110, so a small team gets much further before paying, and it has batching and digests where Siren has none. Siren counters with more channels, broader front-end SDKs, provider pools, campaigns with database connections, and the agent toolkit. On entry economics SuprSend wins clearly. On agent-triggered and human-in-the-loop notification work, Siren is the one built for it.
- **Siren vs OneSignal**: Different buyers entirely. OneSignal is a growth team's tool with push as its deepest channel, its own delivery included, and a free tier generous enough to run a real mobile program. Siren sends nothing itself, assumes engineering, and exists to route product and agent notifications across nine channels through your own vendors. If the question is how to run a push campaign to a mobile audience, OneSignal, and OneSignal can even be the push provider inside a Siren workflow. If the question is how an agent tells the right person the right thing on the right channel, Siren.
- **Siren vs Liveblocks**: Both put an inbox in your product and both stop short of sending email themselves, but the resemblance ends there. Liveblocks generates notifications out of collaboration: comments, mentions, and document activity, with batching, per-user channel settings, and a free plan, from $30 a month once you outgrow it. Siren generates them out of workflows and agent calls across nine channels, with no free tier and no batching. If your notifications are mostly about who commented on what, Liveblocks is both cheaper and closer to the problem. If they are about orders, alerts, approvals, and agent decisions crossing WhatsApp and Slack, Liveblocks does not compete.

## Pairs well with

Siren is a notifications tool, and a team running it still has 6 neighbouring categories to staff. The pick in each is Plain for customer support platforms, Supademo for product onboarding & PLG, Textdrip for SMS marketing, Polar for subscription billing, Kissmetrics for product analytics & session replay and Churnkey for retention & churn prevention, each the leading tool in that category on published criteria.

| Category | Ideal pairing | Because | Benefit |
| --- | --- | --- | --- |
| Customer Support Platforms | [Plain](https://saastracker.org/products/plain) (Momentum) | Siren is built for notifications, not support. Plain adds Slack, Teams, and Discord. | Questions arrive in one queue with a history attached, instead of scattered across personal inboxes. |
| Product Onboarding & PLG | [Supademo](https://saastracker.org/products/supademo) (Momentum) | Siren is built for notifications, not onboarding. Supademo adds custom data residency on Enterprise. | New users reach the thing the product is for without a call, and the drop-off shows up in the data. |
| SMS Marketing | [Textdrip](https://saastracker.org/products/textdrip) (Momentum) | Siren lists 500 stored users on the published plan among its limits. Textdrip adds spintext message variation. | The urgent message gets read within minutes, on the one channel almost nobody ignores. |
| Subscription Billing | [Polar](https://saastracker.org/products/polar) (Momentum) | Siren is built for notifications, not billing. Polar adds best-in-category developer experience. | Recurring revenue bills, retries and reconciles itself, including the tax nobody wants to calculate. |
| Product Analytics & Session Replay | [Kissmetrics](https://saastracker.org/products/kissmetrics) (Momentum) | Siren lists operated by a services studio rather than a funded product company among its limits. Kissmetrics adds transparent published per-event pricing with a falling unit rate. | Feature usage and drop-off are measurable, so a roadmap argument can end with evidence. |
| Retention & Churn Prevention | [Churnkey](https://saastracker.org/products/churnkey) (Momentum) | Siren is built for notifications, not retention. Churnkey adds one vendor and one install. | Accounts at risk surface while there is still time to call, rather than at renewal. |

Pairings follow the SaaSTracker methodology (https://saastracker.org/methodology): the leading tool in each complementary category, chosen on published criteria. Placement cannot be purchased.

## Implementation

- Setup time: An afternoon to a first notification using QuickSend, and a few days to a published multi-channel workflow with templates and a provider configured. The MCP server and agent toolkit shorten the first integration considerably when the trigger is an agent rather than a service.
- Learning curve: Low for engineers. The model is small: users or inline recipients, templates per channel, workflows made of nodes, providers behind them. The concepts that take longest are provider pools and which workspace a key belongs to.
- Onboarding: Self-serve throughout. The seven-day trial unlocks everything, and documentation plus prebuilt templates carry the setup. Pro includes weekday live support; Enterprise adds 24 by 7 cover.
- Migration: Because delivery runs on your own provider accounts, moving to Siren does not touch sending reputation or domain authentication. The work is rebuilding templates per channel and re-expressing existing routing logic as workflow nodes. The item to plan for is anything currently relying on digests, since there is no equivalent primitive and that logic has to stay in your application or be approximated with waits.

## Platform, API & security

- Platforms: Web dashboard, REST API, MCP server, Python and TypeScript server SDKs, JavaScript, React, and Vue web SDKs, React Native, Android, and Flutter mobile SDKs
- API: REST API at api.trysiren.io with a published OpenAPI specification, covering users, templates, providers, workflow triggers (single and bulk), chat sessions, message status and replies, and webhook configuration. Default rate limit is 60 requests a minute with limit, remaining, and reset headers on every response.
- Compliance: None published
- Data residency: Not published. The operating entity is registered in Kochi, Kerala, India, so buyers with residency requirements should ask before evaluating.
- SSO: Team roles and permissions are configurable on both paid plans; no SAML or SCIM offering is published, and member access is described as configurable on Enterprise contracts.
- Security notes: API keys are scoped per workspace, so Sandbox, Staging, and Production cannot reach each other. Webhooks carry a signature header for origin verification and a delivery header for deduplication. No SOC 2 report, ISO 27001 certificate, penetration test summary, or uptime commitment is published, which is the gap most likely to end an enterprise security review.

## Support

- Channels: Weekday live support on Pro, 24 by 7 support on Enterprise, Email and contact form, Priority support during the trial
- Documentation: Documentation at docs.trysiren.io covering workflows, node configuration, every channel and provider, campaigns, cohorts, the agent toolkit, the MCP server, and a full API reference, with an llms.txt index and an OpenAPI specification published for machine consumption.
- Community: Public documentation and a blog; no large public developer community, forum, or open-source repository of the kind Novu has.

## Company

- Founded: 2024
- Headquarters: Kochi, Kerala, India
- Ownership: Bootstrapped. Built and operated by KeyValue Software Systems Private Limited, a product engineering studio running since 2017.
- Employees: Not disclosed
- Funding: No disclosed external funding for the product. The operating company is bootstrapped.

Timeline:

- 2017: KeyValue Software Systems Private Limited begins operating as a bootstrapped product engineering studio in Kochi, Kerala.
- 2024: Siren appears publicly as a multi-channel notification infrastructure product with a visual workflow builder and provider-agnostic delivery.
- 2025: The AI agent toolkit and MCP server ship, repositioning the product around communication for agents, with setup guides for Claude Desktop, Cursor, VS Code, and Amazon Q CLI.
- 2026: The chat node enters beta, adding interactive Slack, Teams, and Gmail messages that hold a workflow execution open until a human replies.

## Integrations

SendGrid, Amazon SES, Postmark, Mailgun, Mailchimp, Gmail, Outlook, and Loops for email, Twilio, Plivo, MSG91, Kaleyra, and MessageBird for SMS, Meta WhatsApp, Twilio, Gupshup, MSG91, and WATI for WhatsApp, Firebase Cloud Messaging and OneSignal for push, Slack, Microsoft Teams, Discord, and LINE for chat, PostgreSQL and Mixpanel as campaign data sources, OpenAI, LangChain, and Vercel agent frameworks, Claude Desktop, Cursor, VS Code, Amazon Q CLI, and other MCP clients

## FAQ

### What is Siren?

Siren is notification infrastructure. It sits between your application (or your AI agent) and your delivery vendors, and owns the routing: which channel fires, in what order, with what template, through which provider, and what happens while it waits for a reply. You trigger a named workflow with one API call and Siren decides the rest across email, SMS, WhatsApp, push, in-app, Slack, Microsoft Teams, Discord, and LINE.

### How much does Siren cost?

There is no free plan. A seven-day trial unlocks everything with no credit card, after which Pro is $249 a month, or $208 a month billed annually, for up to 100,000 notifications, 500 stored users, unlimited workflows and templates, unlimited cohorts, 30 campaigns, 30 days of logs, and four team members. Enterprise is a volume-based contract. You also pay your own delivery providers separately.

### Does Siren send the email and SMS itself?

No. You connect your own provider accounts, so email goes through your SendGrid, SES, Postmark, or Mailgun, SMS through your Twilio or MSG91, WhatsApp through your Meta or Gupshup account. You keep your sending reputation and your negotiated rates, and those vendors invoice you directly. Siren composes, routes, and logs.

### What is the 500-user limit and does it cap how many people I can notify?

It caps how many recipients you store inside Siren, which is what campaigns and cohorts run against. Event-driven workflow triggers can pass the recipient in the payload instead, so a product notifying a large audience by event is not blocked by the number. A team that wants list-driven campaigns to a big audience needs the Enterprise plan.

### Does Siren support batching or digests?

No. There is no batching or digest node in the workflow builder and no mention of one in the documentation. Wait nodes and branching can approximate a delayed single send, but collapsing many events into one summary notification is not a feature of the product today. If digests are the reason you are shopping, look at Knock, Novu, or SuprSend instead.

### What makes Siren different from Knock, Courier, or Novu?

Three things. Channel breadth, with WhatsApp, Discord, and LINE alongside the usual six. Client breadth, with in-app inbox SDKs for JavaScript, React, Vue, React Native, Android, and Flutter rather than React and React Native only. And the agent surface: an MCP server, function-calling toolkits for OpenAI, LangChain, and Vercel, and a chat node that posts an interactive message and holds the workflow open until a human answers.

### Can an AI agent trigger notifications through Siren?

That is the product's main argument. The MCP server exposes sending and workflow triggers as tool calls to any MCP client, the agent toolkit exposes the same as function-calling tools inside OpenAI, LangChain, and Vercel agents, and the chat node lets the agent ask a person a question in Slack, Teams, or Gmail and wait for the answer before continuing.

### Who is behind Siren and is it venture funded?

Siren is built and operated by KeyValue Software Systems Private Limited, a bootstrapped product engineering studio in Kochi, Kerala that has been running since 2017. There is no disclosed external funding for Siren itself. The upside is no investor clock; the downside is a thin public record on customers, scale, and reliability commitments compared with the venture-backed names in this category.

### Does Siren publish SOC 2 or HIPAA compliance?

No. No SOC 2 report, ISO 27001 certificate, HIPAA statement, or uptime commitment appears in the public documentation. Workspaces isolate keys and data between Sandbox, Staging, and Production, and webhooks are signed, but a security review that requires an attestation will need to ask the vendor directly.

### Can I self-host Siren?

No. Siren is a hosted service only. Teams whose requirement is self-hosting or control over where notification data lives should look at Novu, which is open source and self-hostable.

### What should I pair Siren with?

Siren is a notifications tool, and a team running it still has 6 neighbouring categories to staff. The pick in each is Plain for customer support platforms, Supademo for product onboarding & PLG, Textdrip for SMS marketing, Polar for subscription billing, Kissmetrics for product analytics & session replay and Churnkey for retention & churn prevention, each the leading tool in that category on published criteria.

### What do I pair with Siren for Customer Support Platforms?

Plain. Siren is built for notifications, not support. Plain adds Slack, Teams, and Discord.

### Is Siren enough on its own?

For notifications, yes. Siren does not cover product onboarding & PLG, SMS marketing and subscription billing, and its own profile says so; Supademo, Textdrip and Polar are the tools that fill those gaps.

## Editorial verdict

Siren is the pick when the notification problem has moved past email and Slack, and especially when an agent is one of the things doing the notifying. Nine channels, six front-end SDKs, provider pools that fail over between vendors, campaigns with a database connection, and an MCP server that makes a workflow trigger a tool call add up to more product than anything else at $249 a month, and the 100,000 notification allowance is twice what the two closest-priced rivals include. The reasons to walk away are concrete rather than aesthetic: no free tier means you cannot prove it in production first, there is no batching or digest primitive at all, 500 stored users bounds anything list-driven, and no compliance attestation is published. For a small B2B team sending across many channels with an agent in the loop, it is worth the trial week. For a team whose first requirement is a digest, or whose security review needs a SOC 2 report, look at Knock, Novu, or SuprSend instead.

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Source: SaaSTracker (https://saastracker.org), an independent editorial project. This profile is compiled from public information, carries no peer reviews or paid placement, and was last reviewed 2026-09-13. Awards are judged on published criteria: https://saastracker.org/methodology