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Geofencing, battery trade-offs, and spoofing

A geofence asks the system to detect transitions around a circular region without your app continuously polling GPS. It is power-efficient but best effort, not a real-time security boundary.

Define product semantics​

val geofence = Geofence.Builder()
    .setRequestId("site:$siteId")
    .setCircularRegion(latitude, longitude, 150f)
    .setTransitionTypes(
        Geofence.GEOFENCE_TRANSITION_ENTER or
            Geofence.GEOFENCE_TRANSITION_DWELL or
            Geofence.GEOFENCE_TRANSITION_EXIT
    )
    .setLoiteringDelay(2 * 60 * 1000)
    .setNotificationResponsiveness(60_000)
    .setExpirationDuration(7 * 24 * 60 * 60 * 1000L)
    .build()

notificationResponsiveness is a best-effort latency hint. Radius must tolerate real positioning error; a 5-meter fence is generally unrealistic. DWELL reduces rapid enter/exit noise near a boundary.

Transition processing​

Use an explicit PendingIntent receiver/service target. In the receiver:

  1. Parse GeofencingEvent; reject errors.
  2. Validate transition type and request IDs against current durable registrations.
  3. Store event with idempotent identity/time.
  4. Post a user-visible result or enqueue longer work.
  5. Return quickly.

Do not trust that every enter has an exit or that transitions arrive exactly once/in order.

Registration reconciliation​

Keep desired geofences in Room. Re-register when permission/settings/account/configuration changes and after relevant device events. Request IDs are stable domain identifiers; adding the same ID replaces its prior monitored definition.

Room desired fences
        ↓ reconcile
System registered fences
        ↓ best-effort transitions
Durable event handler -> current business rule

Why events are late or missing​

  • location disabled or permission revoked;
  • approximate/background access limits;
  • Doze, device motion/state, connectivity, or vendor behavior;
  • radius smaller than available accuracy;
  • app/package force-stopped;
  • Play services unavailable/outdated;
  • device crosses quickly between observations.
Not proof of physical presence

Geofence and device location can be mocked/spoofed and are probabilistic. Do not unlock doors, approve payroll, or authorize high-value transactions from a single geofence event.

Layered fraud/risk design​

For an attendance app, combine server time, device/app integrity signals where appropriate, prior trajectory/plausibility, Wi-Fi/BLE proximity with consent, account/device risk, and human review. Each signal has false positives and privacy cost. Never silently turn broad continuous surveillance into the default.

Sources​

Exercise​

Design a warehouse arrival reminder and an employee attendance system. Explain why they require different reliability, anti-spoofing, consent, retention, and appeal processes.