The Remote Slave Unit or RSU is a very sensitive microprocessor controlled photo sensor that triggers underwater strobes over large distances. No TTL function is build in the RSU as in the Digital Adapter.

The RSU does not work with active preflashes. Hence in most cases an additional external strobe is necessary to suppress the TTL preflashes of most digital cameras. Under mint conditions distances exceeding 25 meters can be covered with the RSU system underwater. The major application range is creative pool, wreck and cave photography.