Alarm system screwy

'04 Chrysler Concorde: At night only, lights (front and rear) flash on and off for 3-4 times (with red alarm dash light), it will turn off for about 10-15 minutes, then go through the same cycle for 4 hours. Never during the daytime hours. Can be in garage or out, same thing. If you do not lock car (which doesn’t activate alarm), lights do not flash.

Have taken it to Chrysler dealership, they are stumped. Can anyone help me please before my battery dies or car gets stolen?