alarm system went off when car parked and keys removed.

next time, stick the door key in and turn it and that would shut the alarm off- make sure you turn it far enough

I put the key back in crack it and I still had to take the battery cable off

If security light flashes and alarm isn't going off. Shut the door and wait 30 seconds and push unlock on key fob 3 times. Security system light goes back out. And system returns to normal. Computer part of security cannot be bypassed without damaging multiple devices. GM mechanics say faulty sensor on door switches or movement and trunk lock could be setting it off. Find then open circuit and repair that switch. Until you find the one causing the system to go off it will continue the problem.