This class handles geofences managed by various hardware subsystems. It contains the public APIs that is needed to accomplish the task.

The APIs should not be called directly by the app developers. A higher level api which abstracts the hardware should be used instead. All the checks are done by the higher level public API. Any needed locking should be handled by the higher level API.

There are 3 states associated with a Geofence: Inside, Outside, Unknown. There are 3 transitions: GeofenceHardware.GeofenceEntered, GeofenceHardware.GeofenceExited, GeofenceHardware.GeofenceUncertain. The APIs only expose the transitions.

Inside state: The hardware subsystem is reasonably confident that the user is inside the geofence. Outside state: The hardware subsystem is reasonably confident that the user is outside the geofence Unknown state: Unknown state can be interpreted as a state in which the monitoring subsystem isn't confident enough that the user is either inside or outside the Geofence. If the accuracy does not improve for a sufficient period of time, the GeofenceHardware.GeofenceUncertain transition would be triggered. If the accuracy improves later, an appropriate transition would be triggered. The "reasonably confident" parameter depends on the hardware system and the positioning algorithms used. For instance, GeofenceHardware.MonitoringTypeGpsHardware uses 95% as a confidence level.

[Android Documentation]