A system for automatically switching a computer to a password protected screen saver mode when a computer user leaves the proximity of the computer. The system includes a proximity sensor that determines whether or not an individual is located proximate the computer. The proximity sensor interfaces with either the computer a bus bridge, a keyboard controller, a keyboard, or some another component of the computer to cause the computer to start executing a screen saver program responsive to an output signal from the proximity sensor. A variety of proximity sensors may be used, including ultrasound, infrared, or electromagnetic proximity sensors. A proximity sensor may also detect the presence of the computer user by detecting the weight of the user at a location proximate the computer.