 When installing any door window sensor, first locate the raised guides on one side of the sensor, which will need to match up to the raised arrow on the magnet when installed. The gap between the raised markings on the sensor and the raised arrow on the magnet should be less than half an inch. The sensor can be mounted either on the door or on the door jam, provided there is room for the sensor to sit flush to the surface. In the case of a door with molding, you will most likely need to install the magnet on the molding and the sensor on the door. Simply peel the adhesive tape off the back of both the sensor and the magnet and adhere them to the surface. Once again, be sure to align the raised marks on the side of the sensor with the raised arrow on the magnet. The sensor can also be secured to the door or frame using the provided screws for a more secure installation. Make sure to subscribe to our YouTube page and click the Show More tab underneath the video where you can view valuable links pertaining to this product, similar how-to videos, and our low-cost no-contract alarm monitoring services.