Hahnel's Viper TTL Receiver and Transmitter allows users to remotely trigger their flash unit. Multiple receivers will work with a single transmitter, meaning you can trigger multiple flashes at once. The Viper TTL offers full wireless connectivity with the Hahnel MODUS 600RT Speedlight. Control up to three groups of flash guns, each group comprising of one or more flash units. Over 100m range. Compatible with original speedlights and the MODUS 600RT MK II & MODUS 360RT.