Heat alarm with built in 10 Year lithium battery, easy to install, has built in radio frequency technology which allows linking of 20 wireless detectors. · · · Powered by a 10yr Sealed Lithium Battery · · Interconnect up to 20 wireless detectors · · Battery only with integrated RF technology · · Activated by twist and click mounting bracket · · Loud 85dB alarm · · Insect proof · · Test function and hush feature · · Compatible with Hispec Control Unit · · Easy Installation