You can check locking up with a sensor

When you go out, have you worried about the locking of the house? This "leafee mag" monitors the locking of windows or doors by sensors. This is comprised of the main sensor, magnet and mobile application, and the sensor recognizes the distance from a magnet and monitors the open/shut of windows or doors.

For example, if you want to monitor a window, you bond a sensor and a magnet to key lever and sash, then you can use them immediately. The sensor and the mobile application link by Bluetooth, and the application acquires the information of sensors in background. Because you can check the state of sensors when you go out. In addition, these will help prevent a door from being forgotten to close if you bond these to a refrigerator or a air-conditioner. The sensor works by one coin battery for about six months. Startup Strobo is going to release this in November and does pre-sale in crowd funding platform Makuake. They already collected aim amounts of money, but you can still purchase this in 1,480yen - 7,480yen courses. The prevailing price is 1,980yen(Tax not included).

Crowd funding page is here
https://www.makuake.com/project/leafee-mag/