Geofencing sounds technical, but the concept is straightforward: draw a virtual boundary around a real-world location, and get notified when a device crosses it. Here's how Android actually makes that work — and what you should know about accuracy and battery.
What a geofence is
A geofence is a circle defined by a centre point (latitude and longitude) and a radius in metres. When a device enters or exits that circle, the operating system fires an event. Apps register geofences with the OS, which then monitors them in the background — the app itself doesn't need to be running.
On Android, this is handled by the Geofencing API, part of Google Play Services. The OS manages all registered geofences centrally and delivers a broadcast when a transition is detected.
How Android determines your location
Android uses three location providers depending on what's available:
- GPS — most accurate (1–5 metres), but slow to acquire a fix and highest power draw. Only works outdoors with a clear sky view.
- Wi-Fi — uses nearby network SSIDs matched against a database of known positions. Accurate to 15–40 metres indoors and outdoors. Low power.
- Cell towers — least accurate (100m–several kilometres), but works everywhere with signal and uses very little power.
Android's Fused Location Provider blends all three automatically, favouring accuracy when you need it and power efficiency when you don't. For geofencing specifically, the OS skews toward low-power providers to preserve battery — which is why GPS isn't always used.
What affects geofence accuracy
Several factors influence how reliably a geofence fires at the right moment:
- Radius size — smaller radii (under 100m) are harder to detect reliably, especially in areas with weak GPS or sparse Wi-Fi. A 100–200 metre radius is a good starting point for most use cases.
- Urban vs rural — dense cities have many Wi-Fi networks, improving location accuracy significantly indoors and near buildings.
- Device speed— the OS polls location less frequently when the device is stationary to save power. If you drive past a location quickly, there's a small chance the poll missed the window.
- Battery optimization— Android's Doze mode and app standby can delay geofence event delivery when the device hasn't been interacted with. Exempting an app from battery optimization removes this delay.
Battery impact
A common concern with location-based apps is battery drain. In practice, modern geofencing has a minimal footprint because the Fused Location Provider is shared across all apps — the OS coalesces location requests and delivers results to multiple apps from a single hardware poll.
NeuraCue adds no additional background polling on top of what Android already does for geofencing. When no active geofences are registered, the background footprint is effectively zero.
Offline geofencing
Once a geofence is registered with the OS, it continues to work without internet. Location determination using GPS and cell towers requires no network connection. Wi-Fi positioning may be less accurate without network access (since some positioning databases require a lookup), but the geofence will still trigger based on GPS and cell data.
This is why NeuraCue can genuinely claim offline-first functionality — the core trigger mechanism is entirely on-device. See how these capabilities translate into real features, or read more about NeuraCue.