I am new to EZ-B, but if you can toggle a led or switch led on and off with EZ-B, you can switch/control relay. Obviously most probably with transistor. I say this because I got a led toggled on and off with simple speech via the ARC. To replace the led with transistor, resistor and relay should go well.

A TIP 120 transistor lets you use a DO port as a switching port and you can get the power from anywhere.

@ RCStartToFinish

Rex Gordon

Another option you can try is something called a PicoSwitch, and I find it makes things much easier.

http://www.dimensionengineering.com/products/picoswitch

The PicoSwitch is nice. It costs $19.99 + shipping.

Another one that has four relays for $28.95 + shipping can be found here: superdroidrobots.com

The parts for the 2N2222 circuit above are about $2 to $5 depending on where you get them. It just depends on whether you are comfortable building your own circuits (which I love doing for something like this application)

@rgordon I agree the less expensive way is to just build the circuit, but the switch I mentioned just makes it easier (and more expensive)