Energy Star is a US product label for energy-saving devices, building materials, public/commercial buildings or residential buildings. Numerous devices in the IT sector bear this label (e.g. PCs, monitors, printers (peripherals), fax machines, copiers, scanners, multi-function devices).

The Energy Star certifies, for instance, that electrical devices meet the electricity-saving criteria of the US Environmental Protection Agency (EPA) and the US Department of Energy. 

One important criterion in this context is that a device in operation shuts down automatically after a certain amount of time. 

In the case of computers, the processor must power down and the hard drive turn off. Known as “system standby mode”, it results in extremely low energy consumption. Specification 5.0 requires the screensaver to initiate after no more than 15 minutes of inactivity and the system to go into standby (S3 suspend to RAM) after no more than 30 minutes of inactivity.