Martindale-TEK200-Non-Contact-Voltage-&-Magnetic-Field-Detector-Martindale-MARTEK200-P-The-Martindale-TEL200-detects-the-presence-&-polarity-of-magnetic-fields-produced-by-indicators-relays-solenoids-&-transformers-BR-The-integral-self-test-activates-the-sensor-in-the-tip-of-the-tester-at-50 Hz-as-well-as-checking-the-battery-&-LED-This-proves-that-the-unit-is-fully-functional-&-avoids-the-need-for-a-separate-proving-unit-P-P-In-addition-this-unit-incorporates-all-the-capa