Smart Screen On is an Android app which makes the proximity sensor on the phone work as a power button to turn the display ON or OFF by just waving the hand in front of the phone.
Say if your phone does not have any physical button on the front to turn the display on or off, you may use this app to see some notifications or time by just waving hand across the proximity sensor.
Also the app can help prevent the physical buttons from spoiling as they are regularly used.
The app is developed by XDA forum member DDeleted as a sequel to previous app named Smart Screen Off which only turns the display Off.
Not Compatible : This app is not compatible for HTC Desire HD.