Absolutely nothing. Energy Star is a marketing ploy, not a technical specification. Since the manufacturer, NOT a 3rd party 'certifies' the Energy Star Compliance there you are relying on the same people whom are selling you a product to rate if properly.
Search the internet... there is an Energy Star certified alarm clock.. that is GASOLINE POWERED!
http://www.popularmechanics.com/home/improvement/energy-efficient/4350335Technically is supposed to tell you that the device exceeds the 'Federal Standards' for energy use by the class of products. Google it, and its on wikipedia.
