- Battery-free metal tags generate ultrasonic signals when objects move nearby
- Different disc shapes create unique sound signatures that identify tracked actions
- Simulation tools produced hundreds of tag designs for various real-world tracking applications
Researchers at Georgia Tech have built tiny metal tags that record everyday actions without the use of batteries, charging cables or wired power — instead relying on simple movement and sound instead of electronics inside each tag.
Most smart home sensors rely on batteries or wall power, which requires maintenance over time. These tags work differently, using mechanical contact to generate a short ultrasonic signal when something moves.
Each roof sits on a small 3D-printed base that is attached to a solid surface, such as a cabinet frame. A matching tab sits on the moving object. When this object opens or closes, the pin hits the metal disc and creates a short ultrasonic pulse.
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Each frequency a unique identifier
This pulse is too high in frequency for people to hear, but nearby microphones can detect it. A wearable device detects the signal and logs what happened, such as opening a drawer or closing a door.
Shape plays a key role in how tags work, as different cutouts along the metal edge produce different ultrasonic frequencies.
Each frequency acts as a unique identifier that allows a lot of tags to operate in the same area without problems.
“These unique fingerprints can be used for smart home sensing, or what we call ‘activity recognition,'” said Yibo Fu, a robotics Ph.D. student who led the development of tags.
Possible uses range from tracking cabinet access to monitoring water consumption or counting exercise repetitions. Fu suggested tags attached to toilet lids or faucets could help caregivers monitor daily routines for elderly relatives without installing complex hardware.
Interest in the concept grew after Fu shared a video on Instagram (which you can see below) that went viral with over 2 million views.
“There are some pretty interesting comments from people in other fields,” Fu said. “One mentioned the use of tags in filing systems where you have huge shelves and libraries of boxes. When you remove a box or store a new box, there is a quick movement and you would trigger the tags and know exactly what thing you just opened, closed or filed away.”
“Another mentioned tracking locations for thousands of trash and recycling bins in waste management systems.”
Engineers also built simulation tools to design discs that produce specific ultrasonic tones when struck.
Early modeling identified about 1,300 workable designs, and testing used 15 of them to confirm performance.
Ultrasound signals also remain localized, limiting how far the sound travels. Nearby microphones detect activity while remote devices remain unaware, helping to keep the system private and focused on specific areas.
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