I've seen this problem listed elsewhere, but I don't have the same conditions I see others list when the problem starts. As the title says, the car alarm goes off randomly. I wonder if my key fob has gone bad.

I park in my garage, windows down, doors unlocked - so the security system shouldn't be engaged. Key fob stays on the kitchen counter when I'm not out and about, roughly 15 ft from the car with a closed door between.

Last week the alarm would "sometimes" go off when I walked into the garage. At least once I was holding the fob in my palm, buttons facing upward. At some point the remote buttons stopped working (I hardly ever use them, but trying to turn the remote off via fob didn't do anything) and the alarm would only turn off when I cranked the car, and continued after replacing the fob battery. This was happening close to when I needed to schedule 75k mile maintenance, so I scheduled and told them my alarm woes. When I went in for maintenance, the alarm went off as they went to check the mileage (car off, doors unlocked, fob in their hand). The report I got back was that the car was set (stuck?) in "Panic Mode" and they reset (a/the) system and I believe re-paired the fob while changing the fob battery one more time. At that point the remote buttons worked and everything seemed fine.

Until I was at a friends apartment about 8 hours later. I had parked close, maybe 15 ft away from where I was sitting, and the alarm started going off. Fob button silenced it, for maybe 2 minutes. This repeated 4 times until I got in the car to crank it, and the key wasn't recognized so I had to do the magical "touch the key to press the start button" to get the car to start/alarm stop. I drove on home and parked my normal way in the garage. Then I got out with my phone set on stopwatch and stared at the car with the fob (buttons up) in my palm. 45 seconds later the doors locked. I unlocked them and this repeated 3 times, with the same timing. After this I found the remote buttons no longer worked, but after the 4th door lock I got in the car and the key was recognized to start the car without requiring the fob to touch the start button.

My last test - after starting like it's "supposed" to, I left the car door open and took the fob to the farthest point away in the house (at least 4 walls and 40 ft). I came back, closed the door, and started the stopwatch. After 5 min the doors didn't magically lock. I went and got the fob and stood there another 5 min - nothing happened. Remote buttons still didn't work (door handle button to lock/unlock doors still working and recognizing the fob).

With all of that, I want to blame the fob. It's $370 to get a new fob, which feels like the right solution, but I'm open to any other suggestions for what to check. Obviously I have no problems delving into details

 

I would consider attempting to eliminate the FOB from the system.
If you removed the battery from the FOB , and went through the same routine, do you still get the same result.
If you do , I ain't the FOB !
Let us know what you find, thanks.

 

After my original post, I dropped the fob in the kitchen and the alarm started again (no big surprise). The red activation light on the fob was blinking, so I was starting the thing it's just an overly active connection on panic button. The alarm went off 2 more times during the day while I was out. Once when I had the liftgate open and was moving stuff around (fob was in my palm, buttons facing up) and another when I had the passenger door open.

For better or worse, this will be the end of trying to figure it out as traded for a new car at that point.

If there was a good way to diagnose "bad/magically depressed Panic Button on fob" I think that would have been the next step, as it's about the only thing that makes sense for the way it was acting.