PatientOne

Yes I can access all the sensor wires going into the hardwire 16. At the end of line where the sensors are though, they're all embedded in door/window frames and aren't very accessible.

By bypass you mean arm the system with some zones bypassed? Apologies, maybe you can provide more details on how to soak test as you describe.

Running some zones directly to a multimeter is showing between 1.2 and 1.4 millivolts when closed (slightly different for different zones). Running the microwave doesn't affect that. You mean by just unhooking a zone and checking the resistance? With the resistors installed the resistance that I'm seeing appears to be stable, around 3k for each zone. That said the open signals being reported seem to be instantaneous so I'm not sure I'd even be able to observe one on a multimeter if I waited. Currently they're happening every 10-20 minutes. Yep. I would think the problem lines in the QH16 and that the controller just reports whatever is sent to it by the QH16.

Just checked in the attic and the new high voltage line (yellow in the picture below) does briefly cross over some of the alarm sensor wires (white twisted pairs). Some of those wires include zones that have been problematic, but some of the problematic zones come from the other side of the house and do not go anywhere near the new power line. That said, all the alarm wires do bundle together and terminate in near each other.

I forgot to mention, the work that the contractor did in the attic involved running a new 20 amp line for a microwave outlet. Is there a way to detect whether any of the alarm wires are being interfered with by any higher voltage lines?

I have 15 hardwired zones running into a Qolsys Hardwire 16 panel that has been running good for about 4 years. Each zone has 1-4 sensors wired in series with a 3k resistor going into the panel. Recently, I started getting lots of random open and tamper alerts from about 6 zones, all day, including for windows that are never opened. I checked that connections at the panel were secure, tried removing the backup battery, using a surge protector, swapping AC adapters, and even swapping out the panel itself, and the random alerts continue. A multimeter shows the resistance is right around 3k for the zones as expected. In the attic where the wires are run, I did have a contractor working up there recently, but he didn't go near the wires for some of the zones that are acting up and none of the wires look like they were disturbed. That said, the only thing I can think of is that something may be interfering with the wires somehow. Any thoughts on how I can troubleshoot this?