In 1981 I received the Patent on the Bartol Mag-Probe A non-contact instrument that tests AC or DC Solenoid Valves and Relays . The Mag-Probe is sensitive enough to detect the magnetic field generated by tiny "ice cube" relays. Because of the high demand for the High Sensitivity Mag-Probe Bartol Research will only be offering a High Sensitivity Model. This magnetic sensing probe is a completely safe, non-contact probe which allows troubleshooting without schematics or special training while eliminating time consuming and cumbersome hookups. It detects residual magnetism, transient current pulses ("glitches"), in AC and DC-powered solenoids, relays, or any device using a coil. You can safely and easily identify and separate electrical from mechanical problems accurately and inexpensively. Just place the probe tip close to the coil in the device. If the LED is on, the device is energized; if the LED is off, the device is de-energized. The Mag-Probe is constructed of non-conductive materials to reduce the risk of shorting live circuits. It also uses a small internal lithium battery (included) and can be used in situations where lead content is a concern. High-Sensitivity Model HS: Offers a Full Range of Testing, from the Largest Electrically Operated Solenoid Valves and Relays, to Sub-Miniature Devices.