What term describes alerts when a device leaves defined boundaries?

The term that describes alerts when a device leaves defined boundaries is geofencing. Geofencing leverages GPS or RFID technology to create virtual geographic boundaries around a specified area. When a device, such as a smartphone or tablet, enters or exits those set boundaries, the system generates alerts or notifications. This functionality is widely used in location-based services and can be essential for applications ranging from security monitoring to marketing campaigns.

The other terms mentioned do not serve this purpose. Network Intrusion Detection Systems (NIDS) monitor network traffic for suspicious activity, while firewalls are designed to control incoming and outgoing network traffic based on predetermined security rules. Routers are responsible for directing data packets between networks and do not inherently provide location-based alerts. Therefore, geofencing is the most appropriate term for defining alerts related to the movement of devices across established boundaries.