Current testers and detectors check for the presence of current flow in electrical circuits. They are also used to locate current in hidden wires and cables. Measurement type and measurement range are important specifications to consider. There are three distinct measurement types: alternating current (AC), direct current (DC), and both AC and DC. In turn, there are two measurement ranges: AC current range and DC current range. As a rule, the maximum amounts for these ranges are the greatest levels of current that devices can measure. Additional product specifications for current testers and detectors include transmitter operating voltage, transmitter operating frequency, short-mode receiver range short-mode, and open-mode receiver range.