The ISD 2500 series has some issues with false triggers. I had a couple of boards that would go off anytime I flipped a light switch, anywhere in the house. I placed a 0.1 uF cap across the trigger input pin and (I believe) pin 3 on the chip. This solved the problem. One other thing - some fluorescent light fixtures can send some pretty big spikes down the line.
I know you're probably thinking "How does a line voltage spike trigger the chip?". It actually feeds back through the AC powered speakers and the surge fires the chip. BTW, that's another solution to this problem; use battery powered speakers to isolate the sound system. I'll take a look at the boards tomorrow to confirm that cap location.

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But now is the end of days, and I am the Reaper!

Dark Alessa