Pontiac Repair: 2006G6 theft deterant system, theft deterrent system, gm customer

Question
Engine is 6cyl (not GTP) 4dr sedan.  Last night horn started beeping,  I took fuse out to stop.  This AM I saw a light on I have never had seen in 1.5 years of owning the car.  Looked in manual  Theft deterrent system.   Also DIC had door ajar in display.   Could not get door ajar light to go out opened and closed all 4 doors, trunk, hood.  Vehicle has remote start feature.  Noticed when I lock the doors the theft deterrent light now comes on and blink.  Looked in the owners manual and this is normal for a system with theft deterrent.  Went to my dealer, could not get appointment for a few days.  They verified and also with GM customer assistance that my vehicle VIN does not have theft deterrent installed.  That dash light feature is new since last night.   

Now it the door ajar light appears to be off, but I went through and tested it seems as if theft deterrent is active.   I activate,  and I can see light blink every 3 seconds as it should.  If I open door via open window, horn starts to chirp.  

Is this something that is installed on a vehicle, but is not activated but somehow became active on my vehicle.   

Very strange to me

Thank you
David Bach

Answer
Hey David:

These cars all have theft deterant. It's a standard feature. My guess is one of the switches in one of the front doors has gone bad causing all of you issues you just mentioned. it'as a pretty common issue with that car. Easy fix once you find out which door the issue is with. If the car has less than 36,000 miles it's a free warranty repair. Good luck :)