What is geofencing?
Geofencing is the ability to trigger an event when a device crosses a defined geographic boundary — entering or exiting a circle around a point or a custom polygon area. When the user's device crosses the boundary, your app is notified and can take an action: send a notification, record an event, unlock a feature, or update a status.
A circular geofence is the simplest form — a centre coordinate and a radius. Polygon geofences allow irregular shapes: a building footprint, a suburb boundary, or a specific delivery zone. The device's operating system handles monitoring the boundary in the background, which is what makes geofencing power-efficient compared to continuous GPS polling.
Geofencing requires location permission. On iOS and Android, background location permission is a separate, more sensitive request than foreground-only location — and App Store and Play Store reviews scrutinise its use. Your use case needs to be clearly explained to the user.
When does your app need it?
- Workers should be automatically clocked in when they arrive at a job site — no manual punch-in
- You want to notify customers when their delivery driver enters the surrounding suburb
- A notification should fire when a user approaches a retail location or event venue
- Field staff should trigger a workflow step when they arrive at or leave a location
- You need to restrict certain app features to users within a specific geographic area
- You want an audit record of when staff arrived at and departed from each site
How much does it cost?
Adding geofencing typically adds 8–16 hours of development — roughly $1,000–$4,000 AUD.
The simpler end covers monitoring a small number of static geofences with basic entry/exit notifications. The higher end involves dynamic geofences (created programmatically for each job or delivery), polygon boundaries, background location handling, battery impact mitigation, server-side geofence event processing, and an admin interface for managing fence definitions.
How it's typically built
On iOS, geofences are registered with CoreLocation's region monitoring API. Apple imposes a limit of 20 simultaneous geofences per app — a hard constraint worth knowing upfront. On Android, the Geofencing API supports up to 100 geofences. In React Native / Expo apps, expo-location provides a cross-platform abstraction for region monitoring.
For use cases requiring more geofences than the OS supports, server-side geofencing is an alternative: the device periodically reports its location to your backend, which computes boundary crossings. This increases server load and battery usage but removes OS limits.
Background geofencing has battery and privacy implications. iOS can suspend apps in the background; Android may restrict background processing depending on the device manufacturer's battery optimisation settings. Thorough testing across device models is important for reliable behaviour.
Questions to ask your developer
- How many simultaneous geofences do we need? iOS's 20-fence limit is a hard constraint — confirm whether this is sufficient or whether server-side geofencing is needed.
- Does this require background location permission? Confirm the user-facing explanation of why background location is needed, and that it will pass app store review.
- How are geofence events processed? There should be server-side event storage and deduplication — entry/exit events can fire multiple times near a boundary.
- What's the battery impact? OS-native region monitoring is designed to be power-efficient; confirm this approach is being used over continuous GPS polling.
- What happens if the device is offline when a boundary is crossed? Events should be queued and synced when connectivity is restored.
See also: GPS tracking · Maps and geolocation · Push notifications · App cost calculator