The magnetic contact sensor in this gadget works on nearly any type of door or window in your home—refrigerator doors, medicine cabinets, interior and exterior doors, doggy doors, you get the picture—to detect if they've been opened. The sensor can connect to other smart devices in your home and programmed to run an action. For example, if you have the air conditioner on and a window is opened, the sensor can shut off the A/C to help conserve energy. (No need to cool the entire neighborhood!)