Provides accurate testing and monitoring of all AC power source types. Plugs directly into electrical receptical. Fully tests incoming power for: Open Ground, Reverse Polarity, and High/Low Voltage. Advanced microelectronics. RMS voltage and frequency meter. Three LCD display modes with LED backlight show: Alternating Voltage & Frequency; Voltage Only; Frequency Only. Multi-tone fault alarm, hands-free auto reset. Wiring diagnostics. One-button operation.