In her tests, Xu found she was able to pull packets out of the air from target meters between once every 2 to 10 minutes. That's fast enough to be able to work out the average power consumption of a house and notice start to deduce when someone is at home.
"Smart meters should be encrypted," said Xu.
The good news is a new generation of meters based on a more advanced technology, called AMI (advanced metering infrastructure), are supposed to employ encryption. Guidelines from the National Institute of Standards and Technology's Smart Grid Interoperability Panel made such a recommendation in a 2010 report.
"Should designers and manufacturers of smart meters or secondary devices decide to incorporate wireless technology for the purpose of communicating energy usage information, then that data must be securely transmitted and have privacy protection," the report said.
But that's too late for the AMR meters already installed across the U.S.
There are 46 million AMR meters in use in 2011, according to a U.S. Department of Energy report. That represents about one in three houses and businesses. While they are likely to be replaced with AMI meters, the slow upgrade cycle of utility companies could mean they remain in use for years to come.
It's unclear if all AMR meters behave the same way. Xu didn't want to reveal the maker of the meter her team targeted in case it spurs others to try the same thing.
There's also no evidence to suggest that burglars have ever used AMR meters as a way of predicting when a home owner will be present or away, but the research does highlight the potential nefarious uses of electricity consumption data and the need to ensure next-generation platforms are more secure.
A paper describing Xu's research can be found on her website.
Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is email@example.com