Alarm System?
 

Hi, i'm new to the website so excuse my un-experienced knowledge. i just bought a 2005 Cadillac Sts V6 from a dealership, the previous owner had installed a whole bunch of after market equipment like reverse camera blue-tooth pioneer radio etc. so i'm guessing he also installed a after market alarm because every-time i drive my car and get out after 20 seconds or so of the key fob being away it straight ups just locks its self and will unlock it self if i have the key fob with me and the doors are locked. now that's cool & all but today my 8yr old took forever getting out of the back seat and the car had locked before he got out and the alarm went off i hit the unlocked button on the door and it stop but when i tried to leave 30 min later when i hit the push start the alarm went off again, & again & again till i got out the car and hit the unlock button on the key fob, but the thing is, is that the key fob is still the original Cadillac keyfob, is there any thing i can do to make it back to factory alarm? i mean i never seen a car just lock by its self? if someone can give me some insight of what maybe he did or what i could do, to take it back to the original alarm i would seriously greatly appreciate it, thanks in advance.