Godox 16 Channels RT-16 Wireless/radio Studio Flash Trigger with 1x Transmitter + 3x Receiver Set (RT-16 Kit 2) This wireless trigger is control discreteness for camera to trigger hot shoe flashgun synchronously High-speed and synchronous for 1/200 second the radio frequency: 433MHZ (and older can not be universal) working from the outside (open ground)  20-30 meters;indoor working distance  20 meters.