- Battery-free metal tags generate ultrasonic signals when objects move nearby
- Different disc shapes create unique sound signatures that identify actions taken
- Simulation tools produced hundreds of label designs for various real-world tracking uses
Georgia Tech researchers have built tiny metal tags that record everyday actions without the need for batteries, charging cables, or wired power — instead relying on simple movements and sounds rather than the electronics inside each tag.
Most smart home sensors rely on batteries or wall power, requiring maintenance over time. These tags work differently, using mechanical contact to generate a brief ultrasonic signal every time something moves.
Each label sits on a small 3D printed base attached to a fixed surface such as a cabinet frame. A corresponding tab is located on the moving object. When this object opens or closes, the tab hits the metal disc and creates a short ultrasonic pulse.
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Each frequency a unique identifier
This pulse is too high a frequency for people to hear, but nearby microphones can detect it. A portable device records the signal and records what happened, such as opening a drawer or closing a door.
Shape plays a key role in how the labels work, since different cutouts along the metal edge produce different ultrasonic frequencies.
Each frequency acts as a unique identifier, allowing many tags to operate smoothly in the same area.
“These unique fingerprints can be used for smart home sensing, or what we call ‘activity recognition,'” said Yibo Fu, a robotics doctor. student who led the development of the tags.
Possible uses range from tracking access to cabinets to monitoring water consumption or counting exercise repetitions. Fu suggested that tags attached to toilet lids or faucets could help caregivers monitor elderly parents’ daily routines without installing complex hardware.
Interest in the concept grew after Fu shared a video on Instagram (which you can watch below) that went viral with over 2 million views.
“There are some pretty interesting comments from people working in other fields,” Fu said. “One of them mentioned the use of tags in archiving systems where you have huge shelves and libraries of boxes. When you remove a box or store a new box, there is rapid movement, and you trigger the tags and know exactly what you just opened, closed or archived.”
“Someone else mentioned the location of 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.
Initial modeling identified approximately 1,300 feasible designs, and testing used 15 of them to confirm their performance.
Ultrasonic signals also remain localized, limiting the distance the sound travels. Nearby microphones detect activity, while remote devices are unaware, keeping the system private and focused on specific areas.
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