This set of flash accessories includes two Sonia Multi Terminal Slave Units and optical sensors, as well as one Flash Sync Cable. This works by putting your camera into slave mode to trigger other flashes.

Slave Mode is a very useful feature that enables a flash to trigger instantly when the sensor on the front of the unit registers light from another flash. By using Slave Mode you can set up as many extra flash units as you'd like that will all effectively trigger at the exact same time.

These are in very good working condition as I used them sparingly. See pictures!