Examples of RF modules in security products include burglar alarms, fire alarms, personal attack e.g. lone worker alarm system) and elderly/infirm alarm systems (e.g. nurse call).
Alarm systems can be found in many places; buildings, cars and boats. Control applications include door entry systems (buildings, car parks, vehicles etc). Secure control systems may also require encryption.
RF modules are also used in covert activities and can be used by police and other law enforcement / intelligence agencies to monitor criminal activity. CCTV systems can use RF modules for control of the camera.