I once lost my martindale plug in tester and couldn't for the life of me remember last time I had used it so ended up buying a new one...... Some 6 months later was asked to replace some light fittings for an old chap I'd previously worked for, went into little cubby hole to switch electric off only to see blinking green flashy lights ....... On showing customer he tells me he noticed it but thought it was an electric alarm and meant everything was ok...... Been plugged in for 6 months