Knock vs Siren
An independent, review-free comparison compiled by the SaaSTracker editorial team. Both products are profiled in full, and neither can pay for placement here.
Still shortlisting? Browse the best in Notification Infrastructure for every option we track, with award winners called out.
The short answer
Both sides assessedKnock compared with Siren
Siren is the closest thing to a direct challenger at Knock's price point, and it competes on allowance rather than polish: $249 a month for 100,000 notifications against Knock's $250 for 50,000, with nine channels including WhatsApp, Discord, and LINE, inbox SDKs for Vue, Flutter, and Android as well as React, provider pools that fail over between vendors, and campaigns with a database connection. Knock keeps the two things Siren has no answer for: batching and digests, which Siren simply does not have, and a free tier, which Siren does not offer at all. If digests or a long free evaluation matter, Knock. If channel and client breadth do, Siren.
Siren compared with 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.
Choose Knock if
Product and engineering teams at SaaS companies who need real product notifications (in-app feed, digests, preference centers, per-tenant configuration) and want the workflow logic owned by a platform a PM can edit rather than by application code an engineer has to redeploy.
Choose Siren if
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.
Side by side
16 attributes| Attribute | Knock | Siren |
|---|---|---|
| Category | Notifications | Notifications |
| Starting price | $0 (Developer), then $250 per month (Starter) | $249 per month, or $208 per month billed annually (7 days trial) |
| Pricing model | Usage-based on messages sent, with a separate meter for Guide active users and AI agent credits, plus a large free tier and a single published paid plan before enterprise contracts. | 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 plan | Developer includes 10,000 messages a month, 500 Guide active users, 500 AI agent credits, unlimited workflows, unlimited channels, unlimited team members, batching, delays, broadcasts, multi-tenancy, and Google SSO. | No |
| Free trial | No time-limited trial; the Developer plan is permanently free | 7 days with everything unlocked, no credit card required |
| Best for | Product and engineering teams at SaaS companies who need real product notifications (in-app feed, digests, preference centers, per-tenant configuration) and want the workflow logic owned by a platform a PM can edit rather than by application code an engineer has to redeploy. | 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. |
| Setup time | A day to a first workflow in production for a competent backend engineer, and one to three sprints to migrate an existing homegrown notification service. The in-app feed component is typically the fastest visible win. | 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, moderate for product people. The concepts (workflows, recipients, tenants, channels, preferences) are clean, but the mental model of moving decision logic out of application code into a workflow platform takes a team a couple of weeks to internalize. | 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. |
| Platforms | Web dashboard, REST API, CLI, React and JavaScript components, iOS, Android, React Native, and Flutter clients, MCP server | Web dashboard, REST API, MCP server, Python and TypeScript server SDKs, JavaScript, React, and Vue web SDKs, React Native, Android, and Flutter mobile SDKs |
| Compliance | SOC 2, GDPR, CCPA, HIPAA with a BAA on Enterprise | None published |
| Founded | 2021 | 2024 |
| Headquarters | New York, New York, United States | Kochi, Kerala, India |
| Ownership | Venture-backed | Bootstrapped. Built and operated by KeyValue Software Systems Private Limited, a product engineering studio running since 2017. |
| Free tier volume | 10,000 messages per month | None; 7-day full-feature trial only |
| First paid tier | $250 per month (Starter) | $249 per month, or $208 per month billed annually (Pro) |
| Self-hosting | Not offered; managed cloud only | Not offered; managed cloud only |
Strengths and limitations
Knock
Strengths
- Batching, digests, preference centers, and multi-tenancy are all first-class, and they are exactly the four things engineering teams build worst when they build them in-house.
- The free Developer tier is extraordinarily generous, including unlimited workflows, unlimited channels, unlimited team members, and multi-tenancy at $0.
- Bring-your-own-provider means you keep your sending reputation, your existing SendGrid or Twilio contracts, and your negotiated rates.
- Workflows as code with CLI, version control, CI validation, environments, and one-click rollback, which makes notification changes a normal part of the software lifecycle instead of a risk.
Limitations
- Completely unusable without engineering; there is no path where a marketer signs up and gets value, because nothing happens until code calls the API.
- The pricing cliff from $0 to $250 a month with no intermediate plan penalizes exactly the small companies the free tier attracted.
- Guides are metered separately on active users, so the in-product messaging feature has its own cost curve that is easy to miss when budgeting.
- You still pay for delivery separately, and you still own deliverability, list hygiene, and domain authentication yourself.
Siren
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.
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.
Pricing compared
Knock
Usage-based on messages sent, with a separate meter for Guide active users and AI agent credits, plus a large free tier and a single published paid plan before enterprise contracts.
- Developer$0
- Starter$250
- EnterpriseCustom
Knock is priced as infrastructure, and the honest comparison is not against Mailchimp but against the salary cost of the engineer who would otherwise own your notification service. On that basis the free tier is remarkable value and Starter at $250 is fair, since 50,000 messages with batching, preference centers, in-app feed, and multi-tenancy is a quarter of engineering work you no longer do. The weakness is the plan gap: a team sending 15,000 messages a month is paying $250 for capability it barely uses, and the separate Guides meter means the sticker price understates the cost of using the whole product. Add your own provider bills on top and Knock is never the cheapest line on the invoice, but it is usually the one that saves the most.
Siren
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
- Pro$249
- EnterpriseCustom
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.
Editorial verdict on each
Knock
Category LeaderKnock is the right purchase when your notification problem is a product problem rather than a marketing problem. If people are complaining about email volume, if a preference center keeps slipping down the roadmap, if enterprise customers want Slack delivery, or if an engineer already owns a homegrown notification service they resent, this is the layer to buy and the free Developer tier is generous enough to prove it in a weekend. The reasons to walk away are equally clear: there is no marketing surface, nothing works without engineering, you still pay your own providers, and the leap from $0 to $250 a month with nothing in between is genuinely painful for a small team. For a five-person startup, Knock is the first thing to reach for only if you are shipping a product with an in-app notification feed. If your immediate need is onboarding emails and lifecycle campaigns, start with Customer.io, Bento, or Dittofeed and add Knock later when the product notifications become their own problem.
Read the full Knock profileSiren
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.
Read the full Siren profileKnock profile last reviewed 2026-09-07; Siren last reviewed 2026-09-13. Pricing is compiled from public sources and can change without notice. See our methodology.
The best in Notification Infrastructure
9 trackedNotification infrastructure platforms sit between an application and its delivery providers, turning one API call into orchestrated in-app, email, push, SMS, and chat notifications with batching, digests, preference centres, and per-tenant routing, so product teams stop rebuilding that logic in application code.
Batching, preference centres, and multi-tenancy are first-class rather than roadmap items, and workflows-as-code with environments and rollback makes a notification change a normal deploy.
$30 a month for 30,000 workflow runs, or nothing at all self-hosted, against a category whose next cheapest real plan is $110 and whose leader jumps from free to $250.
Founded in 2022 on roughly $1M, SuprSend shipped nine channels on the free tier, CLI environment promotion, an MCP server, and an Agent SDK while larger rivals were still writing about them.
The delivery planner turns cross-channel escalation into configuration: try in-app, fall back to email only if it goes unread, set as a rule rather than written as application code.
A visual designer that previews every channel on one canvas, and a bill that is $0.005 a send with no seats or channel fees, let a non-developer own the message end to end.
Frequently asked questions
6 questionsWhat is the difference between Knock and Siren?
Siren is the closest thing to a direct challenger at Knock's price point, and it competes on allowance rather than polish: $249 a month for 100,000 notifications against Knock's $250 for 50,000, with nine channels including WhatsApp, Discord, and LINE, inbox SDKs for Vue, Flutter, and Android as well as React, provider pools that fail over between vendors, and campaigns with a database connection. Knock keeps the two things Siren has no answer for: batching and digests, which Siren simply does not have, and a free tier, which Siren does not offer at all. If digests or a long free evaluation matter, Knock. If channel and client breadth do, Siren.
Is Knock or Siren cheaper?
Knock starts at $0 (Developer), then $250 per month (Starter). Siren starts at $249 per month, or $208 per month billed annually (7 days trial). The billing models differ, so the entry price is rarely the whole cost. Knock pricing model: Usage-based on messages sent, with a separate meter for Guide active users and AI agent credits, plus a large free tier and a single published paid plan before enterprise contracts. Siren pricing model: 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.
Does Knock or Siren have a free plan?
Knock has a free plan. Developer includes 10,000 messages a month, 500 Guide active users, 500 AI agent credits, unlimited workflows, unlimited channels, unlimited team members, batching, delays, broadcasts, multi-tenancy, and Google SSO. Trial terms: No time-limited trial; the Developer plan is permanently free. Siren has no free plan. Trial terms: 7 days with everything unlocked, no credit card required.
Who should choose Knock?
Product and engineering teams at SaaS companies who need real product notifications (in-app feed, digests, preference centers, per-tenant configuration) and want the workflow logic owned by a platform a PM can edit rather than by application code an engineer has to redeploy.
Who should choose Siren?
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.
What are the best alternatives to Knock and Siren?
SaaSTracker profiles 9 products in Notification Infrastructure. The Summer 2026 awards in the category went to Novu (Best Value), SuprSend (Momentum), MagicBell (Innovation). Every profile is compiled from primary sources, so a shortlist can be built from pricing, limitations, and fit rather than from star ratings.
