If wifi signals were like food — and, let’s be honest, they basically are when going more than a few hours without internet is tantamount to digital starvation — then so-called passive wireless devices would be like a quiet roommate who steals all your food and never pays for anything. Except, in a good way.

See, unlike the mooch who depletes your peanut butter supply one teaspoon at a time and offers guests tea from your stash, digital mooches are great. They don’t need batteries (that die) or power chords (that get lost), because they just harvest energy from the wifi signals already flying all around us. And when they want to send their own signals, they just deflect some of that already-airborne wifi, rather than generate their own — a task too energy intensive to do just on harvested power.

All told, devices — sensors or security cameras, for example — that partake in this kind of digital mooching could use up to 10,000 times less energy than most of today’s devices. You should probably read that again: All told, devices that partake in this kind of digital mooching could use up to 10,000 times less energy than most of today’s devices. So basically, they run on nothing.