Will NOT detect cables behind plaster, buried trunking, etc., and will not detect output from a safety isolating transformers with earthed secondary centre tap. This unit should be checked for correct operation using a known voltage before use. Volt-Stick AC Indicator. Ingenious pocket devices for determining the presence of 50Hz AC voltages. They are battery powered pen style units with nylon tips that glow red when a voltage is detected. There is no necessity for contact or for current to be flowing in order to activate the unit. Ideal for finding breaks in power cables, checking plug wiring, checking fuses, distinguishing between live and neutral wires, determining live cables in junction boxes, finding faulty switches, locating the faulty lamp in a series, and many more. 230V : range 220 to 400Vac (with respect to ground potential). The sensitivity is optimised for detecting 230V 50Hz mains voltages. 110V : range 90 to 400Vac (with respect to ground potential). The sensitivity is optimised for detecting 110V 50Hz voltages as found in factory and other industrial applications.