As far as I know you have to have a compatible switch but they are not as expensive. I originally bought the GE 45609 and would have need this one GE 45610 in addition which is $20 compared to $41 for the single switch. After I had bought the single switch I found out you can use these Lowes Iris switches that are $45 for BOTH switches, $4 more then what I paid for one and appear today be the same switch. I used the lowes switches for my 3 way and the 45609 for a single switch.
From now on though I am buying the lowes brand.
Be careful when you hook up the aux. switch as you only connect the traveler, ground and neutral and tie the 2 power wire together. Otherwise you will destroy the switch.
I hope this helps!