Oh yeah, they built them like bricks back then.

OK. Next idea. How shielded are these devices from RFI?

As an example, I have a security system at my work and earlier this year I started getting tons of false alarms. I mean maddening amounts. At times it was so bad I had to turn off the alarm because I couldn't reset it fast enough.

A clue was the two horizontal lines on some of the security cameras. The lines stayed in the same location, unmoving.

The wiring for these cameras and the affected sensors all ran through a common building. That the interference on camera was synced to the images told me the source of the interference was likely AC line sourced, being locked to the 60hz line frequency.

I did manage to track it down to one location by powering off sections of the building, and I suspected someone was running some equipment that caused it. Eventually that person moved on and of course, the interference stopped and hasn't returned.

Brian