Monitor smart contracts across
every major EVM chain

Ethereum, Polygon, Arbitrum, Base, Optimism — Sentinel watches your contracts on all of them. Event-level alerts for transfers, ownership changes, and pause events. No self-hosting, no infrastructure to manage.

Built for the ops teams securing Web3 treasuries Safe multisigs Snapshot governance Lending markets Token vaults
Start monitoring free How migration works
NETWORKS Ethereum Polygon Arbitrum Base Optimism
What Defender users need to know

Defender isn't leaving you stranded — but it is leaving.

On July 1, 2026, OpenZeppelin retires the hosted Defender platform. Your monitors don't vanish: OpenZeppelin ships free, open-source Relayer and Monitor you can run yourself. That's a real, supported path — a good one if you have the ops capacity.

The catch is the word yourself. Self-hosting means standing up Docker images, wiring KMS for signing keys, running the new stack alongside Defender until you've validated it, then cutting over. For teams that chose Defender because it was hosted, that's a project, not a migration.

Sentinel is for those teams. Give us a contract address; we watch it and alert you. Hosted monitoring that stays hosted.

Event-Level Monitoring

Large transfers, ownership changes, and pause/unpause events — with per-contract thresholds.

Transfers Owner changes Pause / Unpause

Alert Channels

HMAC-signed webhooks and email — get flagged events in your endpoint or inbox with a full dashboard log.

Webhook Email

Multi-chain Coverage

Ethereum, Polygon, Arbitrum, Base, and Optimism — one dashboard for all your chains. No separate tools, no scattered alerts.

5 chains Single dashboard No self-hosting
How it works

Add a contract. Get alerts.

Three steps, no infrastructure.

01

Add your contracts

Paste an address. We watch standard events: large transfers, ownership changes, pause/unpause.

0x4f2a...LendingPool
0x9c3e...TreasuryProxy
0x2f7d...VaultMarket
02

Pick your channels

HMAC-signed webhook or email. More coming.

HMAC-signed webhook
Email delivery
03

Get alerted

Every flagged event hits your endpoint or inbox, with a full log in your dashboard.

Alert with full event log
Dashboard alert history
What Sentinel monitors

Four on-chain events, clearly scoped

Sentinel watches for specific events and alerts you when thresholds are breached. Nothing it can't detect is listed below.

Transfer

Large token transfers above your configured threshold

OwnershipTransferred

Admin or owner key changes on your contracts

Paused

Contract pause triggered by any account

Unpaused

Contract resumed after a pause

What it doesn't (yet): Deep analysis like reentrancy or oracle-failure detection. If event-level monitoring covers your needs, you're in the right place.

Simple pricing

Transparent. No surprises.

Pay once, monitor forever. Cancel anytime.

Starter
$29 /month

3 monitored contracts included

  • ✓ On-chain event monitoring
  • ✓ Threshold-based alerts
  • ✓ Email + Slack webhooks
  • ✓ Daily health checks
  • ✓ Ethereum + EVM chains
Subscribe — Starter
Popular
Pro
$79 /month

Unlimited contracts

  • ✓ Everything in Starter
  • ✓ Unlimited monitored contracts
  • ✓ 15-minute polling interval
  • ✓ Multi-chain: ETH, Arbitrum, Base, Polygon
  • ✓ Custom alert thresholds
  • ✓ Priority Slack + email routing
  • ✓ Alert history & audit log
Subscribe — Pro
Enterprise
Custom

For protocols & foundations

  • ✓ Everything in Pro
  • ✓ Dedicated blockchain RPC
  • ✓ Custom event signature support
  • ✓ Private incident coordination
  • ✓ SLA + response guarantees
Contact Sales

Secure payments via Stripe · Cancel anytime · No hidden fees

What Sentinel watches today: Transfer, OwnershipTransferred, Paused, Unpaused, with per-contract thresholds. Straightforward, reliable, hosted.
What it doesn't (yet): Deep analysis like reentrancy or oracle-failure detection. If event-level monitoring covers your needs, you're in the right place.

FAQ

Common questions

OpenZeppelin Defender retires July 1, 2026. They offer a free, open-source self-hosted alternative. Read the official migration guide →

Supported chains

Ethereum
Polygon
A Arbitrum
b Base
Optimism
5
EVM chains
4
Event types
15s
Alert latency
HMAC
Webhook signing
USED BY DeFi protocols Lending markets Token vaults Governance
Hosted monitoring for Web3 teams

Contract monitoring
that stays hosted

Give us a contract address; we watch it and alert you. No Docker, no KMS, no managing your own stack after Defender shuts down.

Start monitoring free
Ethereum  ·  Arbitrum  ·  Base  ·  Polygon