2012 CR-V alarm going off randomly: which switch is the culprit?

My 2012 Honda CR-V has the factory alarm. Three weeks ago the alarm started going off every few hours. Pressing "unlock" and then "lock" on the key fob would stop the alarm, but a few hours later it would go off again. This even happened when none of the key fobs were in pockets (and so liable to have buttons accidentally pressed). Another symptom: usually, pressing "Lock" on a key fob would lock, then a second "Lock" press would confirm by beeping the horn; this stopped working, so that the second press didn’t beep (I didn’t think to check if the first press still locked).

I disconnected the battery so we (and our neighbors) could get some sleep; when I reconnected it the next morning, the car had apparently repented; the alarm no longer went off, and two "Lock" presses beeped the horn. We talked to our mechanic and he said it’s likely one of the door sensor switches which is getting flaky.

Well, the alarm just went off again. Problem: I counted nine switches which might be involved: four door open switches, four door lock switches, one trunk open switch (there doesn’t seem to be a hood switch). I don’t want to have to replace all of them.

How do I (or my mechanic) figure out which one is the culprit?

Notes:

• As a test of how the alarm was supposed to function, I locked myself into the car, and after thirty seconds the alarm armed itself (the dash light went from long blinks to brief flashes). Then, opening one of the door locks (not even the actual door) set off the alarm.

• I’ve seen a suggestion to disable one of the switches (e.g. the "hood open" switch) so that the alarm never arms itself. Problem: I can’t find a "hood open" switch; the alarm happily alarms itself if the hood is open. The trunk and door open switches won’t work, as if any are open then the alarm won’t arm itself (tolerable) and the locks won’t close (problematic).

• The dashboard has a "door open" display, but it only functions when the ignition is on.