Security alarm/horn going off uexpectedly

I have a 1999 Chevy Silverado 1500 extended cab. Two nights in less than a week, my horn has went off in alarm mode. Is there another reason for this other than an attempted jimmying of the lock? I live in a decent neighborhood with lots of pole lighting. Someone told me the keyfob battery was dying but I don’t have the fob.

I’ve been having problems with the alarm on my 2000 Blazer going off since a close lightning strike last year. The alarm usually goes off after it has been raining for a few hours. Here is a thread I started on the subject.

I lock the door using the key fob or the power door lock switch, then I unlock/lock the driver’s side door using the keys to disable the alarm. The alarm has not gone off since I started following this procedure.

Ed B.