Exactly as it says on the tin, this is a simple black screen with absolutely no clutter so that you can you can turn your screen black without having to lock your phone, which may stop some background apps from working. This also saves a huge amount of battery on AMOLED screens. This app is completely ad-free, and does not require internet access or any special permissions at all, so you can sleep safe knowing that it is not uploading your personal information without your permission. It is also tiny, taking up less than a megabyte on your device.</br></br>