Kidde Firex Smoke Detector, Hardwired with Battery Backup & Front-Load Battery Door, Smoke Alarm (4 pack)

Hardwired 120-volt power source with a 9-volt battery back-up Test/reset button - tests the smoke alarm circuitry & resets memory after an alarm has sounded No low battery chirps; internal timer alerts you to replace the entire unit after 10 years 85 decibel fire alarm alerts of fire Ionization sensor - detects invisible fire particles (associated with fast flaming fires) sooner than photoelectric sensing alarms Constant green LED light indicates that AC power is connected Red LED blinking lights indicate when: alarm is in standby mode, smoke or fire initiated the alarm, or is in hush mode