Tread carefully, per mains monitoring devices.
A nearly useful device for detecting outages was one I purchased a few years ago. Available from Costco, Homebase and other reputable suppliers, it plugged into a 13A socket. When mains power was present it functioned as a motion-sensor ankle level lamp, so useful for dark stairwells and landings. It also contained an internal rechargeable battery and, in event of power failure, illuminated permanently.
We had two of them. All well and good, until one stopped working. Upon disassembly, cause of failure was a wire trapped behind a mounting lug at manufacture. The trapped conductor had eventually fractured, the resulting arcing starting a small internal fire that had caused damage verging upon total combustion of the plastic housing. Examination of the second device showed the same defect, same conductor trapped, just no symptoms yet. Both were taken to the small electrical items/“chinese tat” skip at our local recycling centre.
Both were, of course, legitimately CE marked, and fully compliant with RoHS and other EU standards.