Energy experts have long implored people to unplug electronic devices they aren’t using to avoid “phantom power”—the energy a device consumes even when it’s turned off.

But MIT researchers have now developed a sensor(Opens in a new window) that can save you energy by doing the opposite: leave everything plugged in, and it will tell you which of your electronics (or anything else with a power plug) are using too much electricity.

Though it’s currently just a concept, the sensor could be as easy to install as a light timer: no wires need to be disconnected, and the postage-stamp-sized device can be placed anywhere on an incoming power line.

“We’re trying to lower the barriers to installation,” researcher John Donnal said in a statement(Opens in a new window). “It just goes on with a zip tie.”

Once installed, the sensor goes to work identifying the energy use of everything connected to the grid. Through extensive testing, the MIT team built a catalog of energy footprints for common household, industrial, and even military devices (the research was partly funded by the Office of Naval Research and some of the testing was conducted on board a US Coast Guard cutter). The extensive database will allow a single sensor to identify “signatures” of specific appliances.

MIT envisions that the sensor will be sold with an app that can tell users how much money they’ll save by replacing energy-hogging devices with more efficient ones. Some of the energy use data will be sent to the cloud, but most will stay inside the home, reducing bandwidth demands.

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Besides its ease of installation, perhaps the best part about this electricity sniffer is it won’t require you to open your wallet wide just to save money in the future: researchers estimate the final purchase price to be around $30 once it goes into commercial production.