The ALTA AC Voltage Detection Sensor notifies of the presence or absence of electricity. It is intended for use on devices using supply power from 24 - 500 VAC. Not intended for voltages higher than 500 VAC and also not intended for use with DC sources. Perfect for HVAC systems, sprinkler systems, sump pumps and any other type of electrical appliance monitoring. This sensor triggers on the state change from presence to absence of voltage and vice versa. The data is displayed as either "No Voltage" or "Voltage Detected".