Size: 153 x 25 x 16mm Frequency Range: 50-500 Hz Test Voltage Range: 90-1000V AC Safety Rating: CAT II 1000v Power: 2 AAA batteries With light Detects voltage by inserting into a power outlet and alerts with sound and light. The sound is quite loud, so it can be heard from a distant distribution board, allowing you to turn off breakers and find the corresponding one. How about using it for air conditioner installation? It may react to even faint voltages, so occasionally it may react even after a breaker is turned off. In such cases, confirmation with a proper tester is necessary (these conditions are not defects or malfunctions). We have been using this for over 10 years in air conditioner and lighting work and find it very useful. ※ Although this product is also listed by many others, a considerable number of reports have been made regarding a certain defect. We ship only products that have been fully tested and confirmed to be working.