Elgato Eve Door & Window (1st Generation) - Wireless Contact Sensor with Apple HomeKit technology, Bluetooth Low Energy Know your home: Eve Door & Window understands whether your door or window is open or closed Gain insights: view statistics on time & duration and make smarter choices HomeKit-enabled: unparalleled ease of use and advanced security Works with Siri: ask for the current open/closed state Truly wireless: powered by a long-lasting, replaceable battery Easy setup: direct connection using Bluetooth Smart technology, no hub or gateway required Battery included is a: 1x  AA 3.6V lithium-thionyl Replaceable Battery (type ER14250 or LS1425)