Martindale 13a socket tester with audible warning martindale bz101 safe and simple to use the buzz it from martindale is a real improvement for awkward sockets it has an audible signal to tell you instantly whether or not the wiring is correct and can also be used as a fuse finder as the correct fuse is located when the buzzer stops if there is a problem the pattern of neon lights indicates the fault any results other than three indicators lit and a continuous buzzing tone shows a fau