The Interfit STR203 Strobies Pro-Flash Transmitter/Receiver Kit is used to trigger the Strobes Pro-Flash. With 16 channels, you are able to individually program and group up to 16 Pro-Flash units. Like the Pro-Flash, the Transmitter and Receiver feature simplified controls, letting you adjust the flash power, MF-Assist Beam, Audio Signal and flash triggering all from the camera position. The 165' (50m) working range gives you the freedom to move around and shoot with long lenses, should the situation call for it. The Transmitter runs off of two AA batteries, while the Receiver plugs directly into the Pro-Flash via USB and does not need its own power supply.