t can be mounted on the hot shoe of camera or connected to the PC socket of camera with the cord supplied. Using the PC socket connection (if your camera has one) allows simultaneous use of a hot shoe-mounted flash unit and off-camera flashes with this radio trigger set. There's a test button on the top of the transmitter for test firing. The dip switches for channel selection are on the bottom. There is no power switch. The transmitter is powered by a small 12V alkaline battery. Remove the cover by a small #1 Phillips screwdriver before changing the battery.