Tesla's Sentry Mode records events around your car – but the Tesla app doesn't send you a real-time notification when something happens. You learn about the scratch in your paint the next time you open the app. That annoyed me enough to build SentryBeam: push alerts in under 10 seconds, free, as a PWA on any device.

The Problem

Sentry Mode reliably detects motion and touches, but the data stays in the vehicle or shows up in the app later. For the actual purpose – being able to react while something happens – that's too late. The obvious idea: capture the vehicle events and deliver them as push notifications yourself.

Why Fleet Telemetry Instead of Polling

The classic route via the Fleet API would be polling: querying vehicle state on a schedule. That's slow, burns API quota, and constantly wakes the car – bad for the 12V battery and for latency.

Fleet Telemetry inverts the model: the vehicle streams events to a registered server as they occur. Push instead of pull. That makes sub-10-second latency realistic without bothering the car.

The Architecture

  • Vehicle → telemetry server: the car delivers configured events (including Sentry-relevant states) directly to the server.
  • Backend: filters and interprets events – not every state change is an alarm – and decides when a notification goes out.
  • Web Push → PWA: delivery uses the Web Push standard. The PWA receives notifications on Android, desktop, and – since iOS 16.4 – on iPhone, provided it's added to the home screen.

Why a PWA Instead of a Native App

One codebase, no app store reviews, instant updates. The historic PWA drawback – no push on iOS – fell with iOS 16.4. For a one-person side project, that's the difference between "doable" and "two platform teams".

The Unpleasant Parts

  • Tesla developer setup: developer registration, OAuth flows, key management, and deploying the telemetry configuration to the vehicle. The bureaucratic part took more time than the technical one.
  • Event interpretation: raw vehicle data isn't a ready-made "alarm yes/no". The logic for what deserves a notification took iteration – nobody wants 30 pushes per parking session.
  • iOS web push quirks: works, but only as an installed PWA and with its own rules. Onboarding has to explain that, or iPhone users end up without alerts.

Learnings

  • Push architectures beat polling on latency, cost, and battery – if the platform offers one, take it.
  • The edge of the project is the work: auth, certificates, platform bureaucracy. The core (event in, push out) stood comparatively quickly.
  • Side projects need a real problem of your own. I wanted these alerts myself – that carries you through the dull phases where no feature shines.

SentryBeam is free to use: sentrybeam.app. More projects like this are on the homepage.