The Elcometer 270 Pinhole Detector utilises the ‘wet sponge’ method of holiday detection. When the wand sponge is passed over a pinhole, current flows from the detector through the moisture in the hole to the substrate below and back to the detector via the signal return lead. This current flow triggers an audible alarm and causes the alarm LED to flash. The Elcometer 270 Pinhole Detector is capable of testing at three voltages; 9 V, 67.5 V and 90 V (depending upon model)