The security system of my '98 Accord trips intermittently for no apparent reason. I’m not sure if it’s a sensor/electrical issue or if the car is just getting jumpy in its old age. 
A couple of years ago it started doing this during a cross-country road trip. I got around the issue by disconnecting the battery every time I locked the car, or just not locking it. I took it to the dealer, where they couldn’t easily find the problem, but offered to do a complete test of the electrical system for $300 (no promises that they’d find anything). No thank you!
After several months I started locking my car again and the problem seemed to have resolved itself (my favorite kind of problem). It has been fine since then (for over a year), but tonight the problem started up again.
For what it’s worth, it is below freezing outside, but when this started in 2007, the car wasn’t in any extreme temperatures. The hood latch and door latches seem to be fine, and the car is in a private parking lot away from the street (so not a lot of vibrations from passing vehicles).
In terms of potential fixes, unfortunately the alarm cannot be silenced without also silencing the horn. I believe that the security system is tied in to the radio, so I don’t think I can disable it without also disabling the radio. My best guess is that this is a sensor problem. Does anyone have any other guesses?
Forget the car dealer. They tried to charge me 75 dollars to reprogram the keyless entry/alarm on my Mazda 6-a process that takes all of about 15 seconds. I’d find a reputable local car stereo store that sells alarms and see if they could troubleshoot it or just install a replacement for about 129 bucks. In the meantime just lock your doors manually and use the key to unlock the car.