Specifications: 1. Microphone type: Digital silicon microphone 2. Antenna type: Ceramic antenna 3. Transmission frequency: 2.4GHz 4. Frequency response range: 20Hz-20KHz 5. Transmission time: 20ms 6. Battery capacity: 70mAh (button battery) 7. Charging time: about 80 minutes 8. Working hours: 7 hours 9. Transmission distance: 20 meters (barrier-free)