Glossary
Geofencing
Geofencing defines a virtual perimeter using GPS coordinates plus a radius. In guard tours, it's used to (a) create checkpoints in outdoor areas without physical tags, and (b) detect anti-fraud — flagging a scan performed outside the expected geofence for that checkpoint.
Definition
A geofence is a circular area defined by a center coordinate and a radius (typically 5-50 meters for tour use). Modern guard tour software computes whether a controller's GPS position is inside or outside the geofence and triggers events accordingly. Geofences can be tied to physical checkpoints (validates that the QR scan happened at the right location) or used standalone (creates virtual checkpoints in large outdoor areas).
Anti-fraud use
Geofencing is the primary anti-fraud mechanism in modern guard tours. Without geofencing, a controller can scan a QR code from anywhere — including their car, their home, or a friend's location. With geofencing, the system detects scans performed more than the configured radius from the expected checkpoint and flags them as 'suspicious' or 'invalid'.
Limitations
GPS accuracy varies: 5-10 meters in open sky, 20-50 meters near buildings, completely unreliable indoors. Geofencing for indoor checkpoints (data center white rooms, hospital basements) is impractical — use NFC or Bluetooth beacons instead. GPS spoofing exists but requires device-rooting and dedicated hardware; it's an edge-case threat for most operations.