-9 Wireless Earphone MonitorTransmission System Operating Band: 2.4GHz ISM frequency band. Latency: Stereo Less than 10.8ms, Mono Less than 4.5ms. Effective Range: 30 meters outdoor transmission distance or 20 meters through wall distance. Usage Time: 6 Hours. Battery Capacity: Transmitter 780mA,Receiver 550mA. Soundtrack: Switch to choose Mono/Stereo; (Stereo: green light, mono: blue light.). Support 4 sets of devices work at the same time. Supports one transmission to multiple reception. The receiver has 5 volume indicator lights. 3.5MM interface. color: Black Material: ABS Package Contents: 1 * transmitter 1 * receiver Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.