You'll notice that toward the bottom of the unit, there is a metal spring contact tab protruding from the rear. This is the contact button that you will push to put your 3-way sensor in to pairing mode. But before you do that, you must first put the Vera Smart Controller into pairing mode.
Bring the 3-way sensor to within 3 feet of your Vera Smart Controller. Now firmly press and hold for a count of 3 the metal spring contact tab at the bottom rear of the 3-way sensor as shown:
The red LED on the front of the 3-way sensor will begin by blinking red slowly, then blink quickly to show that the pairing has been made. Release the contact tab by taking your finger off it. The Vera Smart Controller will start to blink rapidly and then return to blinking slowly.
On the VeraLite, press the "+" button and hold it for 3 seconds to save the pairing.
On the Vera3, press the "Z-Wave" button and hold it for 3 seconds to save the pairing.
Your 3-way sensor is now paired to your Vera Smart Controller and ready to be installed wherever you want to put it in your house.