The Boya BY-WM4 is a wireless microphone system for recording audio with an SLR camera or smartphone. You use the microphone directly by turning on the transmitter and receiver and setting the volume level. This makes the Boya BY-WM4 suitable for the novice filmer. Connect your headphones to the 3.5 mm output and listen live. The transmitter and receiver both work on one AA battery. The range of the transmitter and receiver goes up to 25 meters for enough freedom of movement. The transmitter will last about three hours on a full battery.