So you want to make sure you have closed your fridge or it is working properly? The Fridgeye may be able to help. It is a smart sensor that lets you check your fridge’s light status from anywhere in the world. Just connect the app to the sensor, place the device in your fridge, and you are ready to go.
The Fridgeye has a light sensor, circuit board, ABS housing, 9V battery, and iOS / Android apps. The project is getting funded on Kickstarter.