NOVIK NEO VNK 200 True Diversity Professional Wireless Microphone System Headset and Lavaliere Diversity receiver, these transmission system ensure interference-free transmission and minimize dropouts in the RF link, avoid the dead angle. Longest distance in open: 50m (164ft) Headset & Lavaliere Using VHF 200-270 MHz band to avert interference frequency. There is a volt indication circuit in the microphone which can tell you if it is necessary to change the battery.