Includes two door and window sensors Requires eufy Security HomeBase (sold separately) for use Sends alerts right to your phone if a window or door is ajar by 1.5" Siren protection can be turned on and off and when on, triggers a 100dB siren on your HomeBase when forced entry is detected Compact design works on any door or window frame and comes with mounting tape and screws for easy installation options 2-year battery life delivers up to 800 days of monitoring to minimise the need for battery changes eufy is part of Anker Innovations Limited, one of the leading consumer electronic brands in America