For peace of mind in anyones home, these loud 95dB battery operated alarms are a must. Simple to attach to any window or door using the self adhesive backing provided and can be switched on or off. Once an attempted forced entry is made on a window or door the alarm will detect unusual vibrations made by intruders and activate, emitting a high pitched 95dB sound. Each purchase buys you TWO alarms. Each alarm requires 3 x LR44 button cell batteries which are not included. Dimensions are 6cm in diameter and 2cm in thickness.