This software is for you if the power button on your Android device is broken.  Only $2.99 USD is required.

You can wake up your Android device by pressing the volume button rather than the power button if you have this incredibly useful software installed.
GO TO SETTINGS > SECURITY > DEVICE ADMINISTRATORS AND REMOVE THIS APP FROM THE DEVICE ADMINISTRATORS LIST IF YOU WANT TO UNINSTALL IT. After that, you can install the application as usual.
If you're wondering why the app was initially listed as an administrator, it's because only programs with device administrators have the ability to turn on and off the screen. Although you opted-in to this, it's likely that you didn't read the pertinent information when the app requested this permission.