Abstract: A system for managing power states for a video display monitor for a computer during periods of operator inactivity senses the presence or absence of signals provided to the video display monitor for forming an image on the monitor, such as red (R), green (G), blue (B) and horizontal synchronization (HSYNC) and vertical synchronization (VSYNC) signals. Time sensing apparatus at the host senses input activity, and in one embodiment suspends a signal provided to the monitor. Sensing and control circuits in the monitor sense the absence of the signal normally supplied to the monitor, and control power-using circuitry in the monitor in response. In an embodiment applicable to monitors having a microprocessor, the system may be incorporated entirely in software at the host and the monitor. In dumb monitors the system requires add-in or add-on devices cooperating with software.