Wein PS-500-2 2 Channel Pro Sync Infrared Slave Kit H Plug, Transmitter and Receiver/Household.

Pro-Sync provides cordless, remote flash control with virtual immunity to interference. Unlike radio frequency (RF) remote flash control systems, Pro-Sync uses state-of-the-art coded infrared technology to fire remote flash units. Common sources of radio interference, like cellular phones, pagers and cordless microphones (increasingly common at weddings) can disrupt radio flash control signals, but not Pro-Sync.

The transmitter can be mounted on and fired by any standard camera hot shoe (or connected to a PC terminal for off-shoe use). Just slide the compact transmitter onto your camera; no cords, no antenna, nothing to clip to your belt.

Plugged into your remote flash, the Pro-Sync receiver is in a "standby" mode. It easily picks 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. It works indoors or out, with a maximum range of 600 feet (indoors).