Features: LED screen displays noise voltage value and AC voltage value Plug directly into a wall outlet (power outlet), no battery required. Main application: AC communication This measuring instrument is mainly used to measure the frequency-to-noise ratio on 220-240V of commercial power. And through the small speaker inside the instrument, the detected noise is amplified and played out. Specifications Input voltage: AC110V / 220-240V Working environment: room temperature 13 ~ 33; humidity: 0 ~ 80%; altitude below 2000 meters Measuring frequency: 300KHz-700KHz Noise indication: 3 and a half digit black and white LCD digital display Dimensions: 135 X 91mm X 45mm Operation: Plug the power cord into an unfiltered outlet or power strip (120VAC 60Hz).Set the level for a reading of 100.0 on the display (100.0 represents 100% noise level).Without touching the level control, move the power cord to a filtered outlet/power strip and read the relative noise difference.For instance - e reading of 5.0 on the filtered outlet would represent a 95% reduction in the noise level compared to the 100.0 level on the unfiltered outlet.The over-range LED illuminates whenever the display exceeds 199.9. Package Included: 1 x AC Noise Meter 1 x Power Cord Note: The display remains powered up for 30 seconds after power is removed.This feature maintains an active display while moving the power cord from outlet to outlet.