XDA forum member Ddeleted has developed a simple, yet useful app that allows you to control your device's display using its proximity sensor. While some devices have this capability out of the box, many do not. This app aims to fix that.

The way it works is very simple. The application is essentially a toggle--tap the icon to turn it on, after which the display will automatically turn off when the proximity sensor is covered. The app is perfect for automatically disabling the display when you close a flip case or  turn the device face down.

Once you've had enough, simply tap the app's icon again to disable it. Smart Screen Off uses a particular type of wakelock, so the developer assures us that battery drain should be minimal. If anything, this application may end up saving you some precious battery life by allowing you to cut the display without fully locking your device.

In the developers own words:

Smart Screen Off, it's a simple and light app which uses the Proximity Sensor built in your Android smartphone to turn the screen off and on automatically. I decided to code this app when I bought my Galaxy Nexus: this device doesn't have any physical button on the front screen. Being a quite huge phone, it's quite difficult to press the "turn off" button every time I wanted to turn it off and on. So I needed a way to turn the screen off every time I put it into the pockets and off when removed.

Obviously your device is going to need a proximity sensor for this to work but I didn't need to tell you that, right? It's also worth noting that this doesn't lock your device, it simply turns off the display.

The app is free and can be found in the application thread.