If the battery has been disconneted,the taildoorglass will need to be recalibrated. if the alarm was armed when the battery was disconnected (or discharged) disarm the alarm after reconnection-the glass will fully lower. this will happen automatically if the alarm was in a disarmed state when the battery was disconnected. after battery reconnection, fully raise the glass-the taildoorglass is now recalibrated(if the glass is not fully raised an error beep will sound , hope this helps.