Flash Slave Trigger, hot shoe, PC, infrared, tripod socket
This infrared flash trigger with a hot shoe is actually two products in one.
It's got a cold shoe that slips into a standard metal shoe like the one that you'd find on a camera bracket.
It also has a female PC connection on its side that can plug into a camera or another flash.
Alternatively, a 1/4"-20 brass tripod socket is tapped into the bottom of the shoe, which allows you to mount it onto a light stand or a tripod.
The IR sensor in this unit will recognize a typical small flash up to 70 feet away and trigger a second flash that is connected to the shoe.
It will also trigger a third flash through the PC connection via a cord.
$15 + $5 shipping