06 Cobalt, think I figured out the problem! I was installing hids and left my window down incase I left my keys in the car bc IV locked my keys in so many times I just don't trust it. I reached in without opening the door through the driver window and started the car will the car was armed and I think it reset the locking problem bc the alarm dissent go off now when I open the door. Try it out and let me know!

 

Unlock the car roll the window down and shut the door wait until armed and reach in and start with out opening the door.

 

Hello, I am having a similar issue w/my 2005 Cobalt. This week I was driving and my locks started locking and unlocking on their own (the automatic lock hasn't worked in a long time). Next, when I would open the door and/or the trunk the alarm (which I don't have a key fob for, and therefore have never used the alarm) would start sounding w/the alert sound, and if I didn't put the key in quickly enough, the alarm would go off until I started the car. Yesterday, I opened the passenger side door (I hadn't locked the doors when I got out of the car, so they locked on their own) put all of my things in the car, and started it, shut the passenger door, walked over to open the driver door and I was locked out of the car w/the car running and all of my belongings inside my running car. Thank God for AAA!! Any idea whats going on w/this? I am not good w/cars, and neither is my bf. I'm hoping for a quick/easy self fix...

 

Just noticed ej7227's comment on turning on the 06 cobalt while the door is shut/locked. I'm going to give that a try tonight. Fingers crossed!!!

 

I had the exact same situation and fixed it on my 06 cobalt !!!! beforehand my door locks would "ghost" lock and unlock randomly even while driving it was really annoying when I got locked out to have to wait to get back in. Anyyyywayys. The alarm always went off after 30 seconds of the door being closed and reopening it or trunk ect. It's the door lock. I just took a screw driver five min ago took out the two screws holding the lock in and disconnected it. Problem solved!!!!!!!!. Took me five min and a Phillips head screwdriver. At least until I get a New lock switch. Hope this helps you or if you got it fixed someone else!

 

I have a 2009 cobalt and the alarm goes off in the middle of the night for no reason, well I am sure there is one I just do not know it. It has happen 3 time now but not every night and not any where else.