When you driving car or motorcycle, for both wearing helmets, or the speed is very high, or to exercise various situation in a very noisy place, use this interphone can effectively communicate with the other one to avoid head turning problem. Specification: Power supply: 2 x AAA batteries(not included) Frequence: 50-20000Hz+3 db Working Temperature: -20°C~50°C Dimension: 63x50x25mm Weight: 150g