Just bought one of these
Reviews seemed good only needed it to confirm circuit is off before I cut i nto it. It seems to detect voltage but when I switched the circuit off it s till seems to think there is voltage although the beep / led is not continu ous. I know the socket is off as I had something plugged into it which then went off when I switched the circuit off.
The instructions say that it self tests when you press the power button and indicates ok with a flashing LED. Mine gives a solid green.
Just took it back to Screwfix and tried 3 others and non seem to do the sel f test thing. Brought a new one home to test on the off circuit and same pr oblems.
It seems unlikely that all 4 and dead (maybe a dodgy batch) but now thinkin g maybe I am missing something?