Tracing a weird signal in an old house taught me to trust my ears...

I was on a job last week at this really old place with thick plaster walls and weird wiring everywhere... The homeowner kept getting false triggers from a hallway motion detector, and nothing in the panel logs made sense. Back when I started, we didn't have all these fancy diagnostics, so you had to listen close for any odd sounds on the line. I dug out my old tone generator and probe from the bottom of my kit, something I hadn't touched in ages, and started following the wire. Turns out the problem was a shared junction box with an ancient doorbell transformer that was leaking just enough voltage to confuse the sensor. It took me back to my apprentice days, walking lines with a simple amplifier and a pair of headphones. I sorted it by rerouting the transformer to its own circuit, and the false alarms quit right away. Sometimes the old ways still get you out of a jam, even with all the wireless stuff we use now.