An easy to use electronic entrance-monitoring device, which creates an invisible infrared beam between the two units up to 4 metres or 20 metres apart. Alarm sounds when someone moves through the beam, i.e. alerting a carer if someone has wandered from a bedroom at night. Three volume level settings and alarm tones. Easy to install, no fixing required. Easy to align with LED indicator lights on both units. Each unit uses 1 x 9v battery (not included) with low battery warning signal.