This wireless audio baby monitor uses sound. Install two “AAA” batteries for Receiver and Transmitter. Volume is adjustable. Place the Transmitter near the baby, and place the Receiver at any location, even in your pocket within the cover range of signal (The LED light will always flash one time every 10 seconds, if out of signal cover range the LED will not flash), Once the baby is crying or making sound, the receiver will activate. Please change the batteries if the products out of services. The products are not toys; please keep out of children’s touch.