Quantum Radio Slave 4i provides coded radio signal that works indoors, outdoors, around corners and through walls. Line of sight is not required between Sender and Remote. Trigger any number of remote flashes without a sync cord. Trip a motor drive camera, or a remote power pack at great distances. Unlike other types of slaves, Radio Slave 4i cannot be overpowered by the light of a flash. Status lights on both Sender and Remote confirm proper operation and/or low batteries. This product is a frequency D Sender only.