The Yale Security Easy Fit Smoke Detector is suitable for connection to Easy Fit alarm systems. It will activate the house alarm in the event of a fire. It also has a built-in siren that sounds on the device when smoke is detected. The smoke detector is easy to fit and includes a test button for range testing. Radio: 868MHz FM. The pack contains: 1 x Smoke detector (with bracket).2 x Wall plugs and screws.3 x AA Alkaline batteries.