Sometimes my stock alarm works....I dont hear the little beep when i lock the door from the inside.....its works sometimes....like everyonce in a while....but when i unlock the door i see the security light go on but when i lock it it doesnt go on.....what could be the problem with that system???

 

if something isn't closed all the way (like the hood/trunk/doors) it shouldn't arm.

Also sometimes the switchs on the inside of the doors, the contacts get dirty. That will cause falsing (the alarm being set off by itself) and not arming. To fix that, just clean the lock switch that is built into the door release inside.