Does Xfinity home security use magnet sensors? Please see below
The contact sensor used, which is designed to set off the alarm when a door or a window is opened, works by detecting a magnetic field emitted by a magnet mounted on the door or window. During the experiment, Kaspersky Lab experts were able to use a simple magnet to replace the magnetic field of the magnet on the window, allowing them to open and close a window without setting off the alarm. This vulnerability is also impossible to fix with a software update; the issue is in the design of the home security system itself. Furthermore, the magnetic field sensor-based devices are a common type of sensors, used by multiple home security systems on the market.
http://www.infosecurity-magazine.com/news/coffeemakers-baby-monitors-iot/