The Speedotron DS-1 Digital Flash Trigger works as an ordinary slave sensor, which will syncronize immediately with a master flash. Designed to also work with digital cameras - which use a pre-flash mode - this slave sensor can be switched from Normal Flash to Pre-Flash syncronization.
Since ordinary slave units will not work with most digital cameras (because these cameras use a very rapid series of pre-flashes, that trigger the slave prematurely), this slave has been optimized to also work with digital cameras.