Shwetak Patel, 27

Walls can talk, and Shwetak Patel, an assistant professor of computer science and electrical engineering, captures their stories: tales of how people move through their homes and how they use electricity, gas, and water. Patel has shown that each electrical appliance in a house produces a signature in the building's wiring; plugged into any outlet, a single sensor that picks up electrical variations in the power lines can detect the signal made by every device as it's turned on or off. This monitoring ability could be particularly useful for elder care, but there was previously no practical way to achieve it, because it would have required numerous expensive sensors.

Last year, Patel did something similar with ventilation systems, designing a sensor that detects subtle changes in air pressure when a person leaves or enters a room. More recently, he's shown that slight pressure changes in gas lines and water pipes betray the use of specific appliances or fixtures, such as a stove or faucet. Patel believes that providing people with information about their patterns of resource consumption can help them reduce it. He has cofounded a startup that will provide consumers with utility bills itemized by appliance. --Kate Greene

1. Anything plugged into an electrical outlet--DVD players, TVs, lamps--displays a unique signature when turned on or off. Even identical light bulbs in different rooms produce impulses with distinct shapes.

2 and 3. Ventilation systems can be used to detect a person's location. Opening or closing a door, or even stepping into a doorway, c­reates slight variations in air pressure that can be detected by a sensor installed in an HVAC control unit.

4. Gas lines that connect to water heaters and stoves can be outfitted with sensors that record changes in pressure when each appliance is used.

5. People's locations and activities can be inferred from the lights they turn on and the appliances and fixtures they use. This information could be used to monitor elderly or infirm people without employing a complicated collection of expensive motion sensors.

6. Even identical toilets in different parts of the house produce distinct pressure signatures in the plumbing.

7. Just as a single sensor in an electrical outlet can distinguish various electronic devices, one pressure sensor connected to a cutoff valve or an exterior water bib can distinguish different water fixtures, such as showers, sinks, and toilets.

Credit: Bryan Christie Design