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 dbWorking Temperature: -20°C~50°CDimension: 63x50x25mmWeight: 145g