PoolGuard Wireless Door Alarm will sound immediately when a child opens the door and the alarm will continue to sound if the door is left open. If a child goes through the door and closes it, the alarm will sound for 5 minutes and then auto-reset. The Poolguard Door Alarm features a wireless transmitter that allows adults to enter the home from the outside with the alarm sounding. This door alarm is always on and will automatically reset under all conditions. As an added feature, the Poolguard Door Alarm is equipped with a low battery indicator that audibly alerts you when the battery is getting low. This door alarm uses one 9-volt battery (not included).