The Hot Shoe Flash Remote Trigger Sensor SYK-4 is harnessing optical theory making the master flasher to control remotely the auxiliary one to flash synchronously without the need of connecting wires. It features small in volume, good-looking in exterior, high in flexibility and stable in performance, it can also artificially create different kinds of effect and take special.The remote slave trigger is suitable for all Flash.Work with most flash units using universal hot shoe like Nikon, Sigma,Olympus, Pentax except Minolta/Sony as they use a special hot shoe, except Canon as they use special triggering voltage.With the high sensitive light sensor of this remote slave trigger, the speed flash can be triggered by the master flash easily. It adopts optical theory making the master flasher to control remotely the auxiliary one to flash synchronously without any connection wires. When this remote slave trigger senses another flash firing in its proximity, it triggers the flash attached to it. This slave trigger gets its working power from the flash attached to it and therefore it is battery-free. This remote flash trigger also supports red eye reduction function.