The hahnel viper wireless flash trigger allows you to individually control up to three groups of canon dedicated flashguns from your canon eos dslr with each of those groups comprising of one or more flashes the easy to use lcd panel allows you to control each of these groups turning the power on or off adjusting the output or setting it to manual allowing the output from the light source to override the viper both the transmitter and receiver are powered by two aa batteries and additional