Never replace batteries for the 10-year life of the unit! Sealed-in lithium power supply eliminates concern about battery removal or unauthorized alarm deactivation. Quick and easy to install; alarm automatically activates when attached to the mounting bracket with no pull-tabs or switches. Smart Hush™ feature temporarily silences nuisance alarms. Includes ionization sensor, test button, low battery signal and flashing LED power light. Maximum Height: N\A; Battery: Lithium Ion; Wall-Mountable: Yes;Universal Mounting Bracket: Yes.