The Wein PSR-500-2E is the 2-channel Receiver in the Pro-Sync series. An unlimited number of Pro-Sync receivers can be triggered by a Pro-Sync transmitter set to the same channel.
Plugged into your remote flash, the Pro-Sync receiver is in a "standby" mode. Pro-Sync receivers can easily pick up the signal from behind backdrops, soft boxes, even around a roomful of wedding guests. Nothing else can trigger the receiver, not even a full-power flash fired inches away. They work indoors or out, with a maximum range of 600 feet (indoors).
The receiver draws power from the flash to which it is connected; there are no batteries to change on the receiver. This receiver is a phono plug sync type. Receivers are also available with Female Household (2 prong) connectors, so they connect directly, cordlessly, to most professional flash units or power packs. For additional versatility, each receiver also has a standard PC terminal.