Sentinel · Apple Watch
A sensor crosses the line.
Your wrist knows first.
Pair a $15 Bluetooth thermometer and Sentinel alerts you on the wrist the moment a reading crosses your threshold — fridge, freezer, fermenter, server closet. No app open, no account, no subscription.
Features
Quietly watching. Loud when it matters.
Background BLE alerts
Fires the instant a reading crosses your line — even with the app closed and the phone in another room.
Works with cheap sensors
Standard Bluetooth thermometers and hygrometers, the ~$15 kind. No proprietary hub, no cloud.
No false alarms
Hysteresis and debounce — the same logic behind ChargeGuard — stop a value hovering at the line from spamming you.
Glanceable status
A complication shows the current reading and a safe / warn / alarm state at a glance.
How it works
Three steps, then it's just there.
Pair your sensor
Connect a standard Bluetooth thermometer or hygrometer in a tap.
Set a threshold
“Alarm above -15°C.” Add hysteresis so it won't nag at the edge.
Get the buzz
Cross the line and your watch buzzes — fix it before the food, or the server, does.
Screenshots
See it on the wrist.
Design preview — final App Store screenshots before launch.
Pricing
One price. Yours forever.
A single one-time purchase — buy Sentinel once and keep every feature for good. No subscription, ever.
Sentinel One-time
$4.99 · one-time purchase · yours to keep
- Background BLE monitoring
- Custom thresholds + hysteresis
- Multiple sensors
- Safe / warn / alarm complication
- No account, no subscription
FAQ
Quick answers.
Do I need my phone nearby?
No. The watch monitors the sensor over Bluetooth in the background — no app open, no phone required.
What sensors work?
Standard BLE temperature/humidity sensors — the inexpensive kind — plus common vendor profiles.
Is there a subscription?
Never. Sentinel is a one-time $4.99 purchase with no account and no cloud.