The Interfit Remote Radio Trigger allows users to remotely trigger the F121 series flashes and is also compatible with most cameras. The trigger attaches to the cameras hotshoe and works on a radio frequency. The Interfit F121 Remote works on 4 channels and offers a test button plus a 3.5mm jack socket.Specifications:Compatibility: Interfit F121 100w and 200w studio flashChannels: 4 (1, 2, 3, 4)Maximum flash synch speed: 1/250 secTransmission range: 100mPower supply: MN21 12V A23 / V23GA / 3LR50