Honda Accord Alarm Problem

My 2001 Accord SE alarm goes off at random times. The lights flash and the horn honks for hours at a time. My mechanic and the Honda dealer can’t find anything wrong with it. We tried disabling the alarm, but then we couldn’t roll down the electric windows. So we disconnected the horn, but the alarm still goes off with just flashing lights. I need my horn back and I’m afraid the flashing lights will wear down the battery. Any suggestions?

Is this alarm original equipment or did someone install it aftermarket?

It’s original and apparently integrated into the electrical system. That’s why it got funky when he tried to disconnect it.