Use the Radio Slave 4i to synchronize any number of remote flashes without long sync cords, or, connect Radio Slave to trip motor drive cameras at great distances. This most popular radio trigger uses digitally coded signals that work indoors, outdoors, around corners and through walls. Unlike other slaves, it cannot be overpowered by the light of a flash. The Radio Slave system syncs at up to 1/500 sec. with focal plane shutters and 1/1000 with leaf shutters. Radio Slave is virtually indistinguishable from "wired" sync, and there is no waiting between triggers as with infra-red slaves. When mounted on a camera hot shoe, the Sender unit get it"s shutter sync withoutexternal cords. The Remote units connect directly to flashes using the flash sync cord. Adapters are not needed. Radio signal confirmation is assured by Radio Slave"s status light. It also warns hours in advance of low battery. Battery life of the Remote is 400 hours with alkaline or 800 hours with lithium AA cells. The Sender unit"s battery lasts 1-2 years! Each Radio Slave has 4 channels of operation and comes in one of 4 discrete frequencies, to avoid interference from other shooters. Take RadioSlave from studio to wedding hall to coliseum. Radio Slave 4i is compatible with the Radio Slave 4 and Radio Slave 2. Be sure to match the labled frequency (either A,B,C, or D) with your previous units. (Radio Slave is not compatible with FreeXwire.)