... long distance 500m 1V3 1,2.4G ISM Public Frequency Band:2402MHz-2479MHz 2,Transfer rate:250K wireless voice door phone for long distance 500m 1V31,2 ... ,workshops,homes,buildings ect.Using the 2.4G Communications Channel, full-duplex interoperability intercom, communication distance up to 500 meters aboveInstructions:1 ... beeps, re-timed one minute. wireless voice door phone for long distance 500m 1V3