Okay, I accidentally left my dome light on in my S2000, and it completely ran the battery dead. I hooked up a charger to the battery, and when I got in my car and shut the door to test it, I noticed that my door ajar beeper was going off, even though the door was shut, the key was off, and the lights were off. So I opened the door, and the beeping stopped. I turned the lights on, still no beeping. I closed the door, still no beeping. I turned the lights back off, and it started beeping again. Basically, it beeps when the door is closed and the lights are off, but if I turn the lights on and/or open the door, it quits beeping. The only wiring I've messed with is an auxiliary cable to hook up to my MP3 player from my head unit. Is it possible that I messed up some wiring under the dash in doing that that'd cause this issue?

 

Apparently it was the fault of the battery being almost dead. The battery's charged now, and it's acting like it should now.

 

Has this happened again? My '08 has been doing something similar, but not exactly the same. When I turn the car off and remove the key, then open the door to get out, the car beeps at me as if the head lights are turned on. I check to make sure everything is off, then close the door and the beeping quits. Even if I let the car sit in my garage over night, it will start beeping again when I open the door to get in and go to work. It doesn't do this all the time, so I have NO IDEA what is causing the thing to beep!

 

Yours is a different issue, some fo the Ap2's do this. Its your key cylinder thinking the keys still in when you remove it. Turn the key off on a couple times and it will shut off.