DESC: Protect your family with this sensitive loud alarm; connects directly to your homes electrical system for continuous function plus with a battery backup in case of outages, Stateoftheart ionization sensor; fast and easy installation, Hush button lets you quickly silence false alarms; lowbattery signal offers peace of mind, Interconnects with up to 24 Kidde devices 18 of which can be initiating including smoke carbon monoxide and heat alarms, 5.5" dia.