The PocketWizard Plus II Transceiver/Relay is a triggering system that offers Auto-Sensing Transceiver Technology. This technology analyzes the status of the Plus II's miniphone jacks, camera hot shoe or the TEST button to determine which mode (Transmit or Receive) to set itself. By default, the Plus II is always in Receiver mode unless it senses a trigger pulse from a camera's hot shoe. It then quickly switches to Transmitter mode. The Auto-Sensing feature can also be disabled, if necessary.