Hi @ainejo. We have some tips on how to install Contact Sensors on different types of doors, windows, and trim [here](https://support.ring.com/hc/en-us/articles/360018549231-How-to-Install-your-Ring-Alarm-Sensors-on-Different-Types-of-Doors-Windows-and-Trim). The Contact Sensor has a sensor in one piece, and a magnet in the other. These two parts have to be close enough together when the door or window is closed to register as closed. Once the two parts are brought far enough away, such as when the door or window is opened, that's when the Contact Sensor is registered as open.