Car Alarms: theft, chevy impala, bezzle

Question
My car just got broken into and it puzzles me on how. I have a 2001 Chevy Impala LS. They broke into my car by inserting something into the driver side key hole. I can tell by the scratch's it left on the bezzle. I understand (I Believe) how the factory alarm system works (To unlock the car with the key would cause the alarm to disarm). I guess my question is what did they use and/or how come my alarm did not go off. I was at work at the time of the theft. My car was in within range of someone hearing the alarm go off. My battery was never disconnected because the time was correct. Please help to put my mind to rest on this matter hopefully to prevent it from happening again. Thank You Leon

Answer
Hard to say what they used. If the factory alarm (OEM) was
triggered, the horn would honk, and the headlights would flash. If it was an aftermarket alarm, it would have it's own siren, and flash the parking lights ONLY.
That being said, if you did not have a remote for the
FACTORY alarm, the key would have turned off the alarm
if turned all the way left, then right. This would
manually disarm the alarm (FACTORY) If aftermarket, it
would have triggered if armed, when the door opened if installed correctly. From what you've said, this is not the case.

Without the chance to inspect it, I can not provide
a final answer as to what had happened. You have a remote?
If so, is it the one that came with the car? Is it GM's
or is it an aftermarket brand? Please give me some more detail so that I can determine what actually failed here.

ALARMTEK