Circuit tracers or signal tracers are used to troubleshoot circuits. They are relatively simple electrical testing instruments that enable electricians and other users to locate, trace and identify common electrical problems such as breakers, shorts, and open circuits. Some circuit tracers can locate wires behind walls, under ground, and inside junction boxes. Others are designed to find blown fuses or test light fixtures. Circuit tracers and signal tracers that can locate neutrals, ground faults, and high voltage lines without power interruption area also available. Most products are capable of continuity checks and audible continuity measurements. Continuity checks test a circuit for completeness. Audible continuity measurements beep when probes touch each other.