According to researchers, this could help cut energy bills and significantly reduce people's carbon footprint.
The software has been developed by Peter Hopton of Sheffield, UK, and launched by his company VeryPC last week.
The system uses open-source face-detection software linked to a webcam to monitor the presence of someone's face in front of the screen and react to it.
While computer users can set their screens to sleep after a set period, many users override this because it interferes with the way they use their computer.
"If you are watching video with your screen saver set to kick in after 15 minutes, that is going to interrupt your viewing, so you disable it. Once disabled, the settings tend to stay that way," New Scientist quoted Hopton as saying.