When you receive the additional sensor in the mail, it will include a card directing you to activate the sensor via the Setup Wizard on the Frontpoint App. You can access the Setup Wizard by logging in to your Frontpoint App and selecting the Equipment Setup option in the menu. From here, select the category of the equipment and a list of all the available pieces of that type will appear. Then select which ones you are ready to activate and the app will walk you through activating, mounting, and testing the new equipment.