Help Me Identify This Mystery Device

[JustinAtSense]

That would be my guess - I’ve seen a few defrosters operating in similar frequency and pattern looks like a heating element.

Refrigerator Defroster

Yes. agree. I checked back several weeks - its exactly the same waveform, 8 cycles over about 35 mins, every 4 days. i thought maybe a charger system I have on a parked car for winter - but not able to trigger it.