Eizo Nanao has announced the inclusion of a "EcoView Sense" feature into their just announced FlexScan monitors; the 20-inch EV2023W and the 23-inch EV2303W.
The EcoView feature, allows the monitors--using motion detectors--to detect if a person is sitting in front of it.
If it senses for 40 seconds that no one is there, it puts the monitor into sleep mode. It then resumes normal operation when the user returns. For example, it won't be fooled by such shenanigans as leaving a cardboard cut out of yourself in front of it. It will only resume if there is movement up to 120 centimeters in front of it.