- Battery-free metal tags generate ultrasonic signals when objects move nearby
- The different disc shapes create unique sound signatures that identify the actions tracked.
- The simulation tools produced hundreds of label designs for various real-world tracking uses.
Georgia Tech researchers have built small metal tags that record everyday actions without the need for batteries, charging cables or wired power; Instead, they rely on simple movements and sounds rather than electronic devices within each tag.
Most smart home sensors rely on batteries or the power outlet, requiring maintenance over time. These tags work differently: They use 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 above the moving object. When that 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.
That pulse is too high in frequency for people to hear, but nearby microphones can detect it. A wearable device records the signal and records what happened, such as opening a drawer or closing a door.
Shape plays a key role in how labels work, as different cuts along the metal edge produce different ultrasonic frequencies.
Each frequency acts as a unique identifier, allowing many tags to operate in the same area without problems.
“Those 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 labels.
Possible uses range from tracking cabinet access to monitoring water usage or counting exercise repetitions. Fu suggested that labels attached to toilet lids or faucets could help caregivers monitor elderly relatives’ 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 more than 2 million views.
“There are some pretty interesting comments from people in other fields,” Fu said. “One mentioned the use of labels in filing systems where there are huge shelves and libraries of boxes. When you remove a box or put a new one away, there is a quick movement, you activate the labels and you know exactly what you just opened, closed or filed.”
“Someone else mentioned tracking thousands of trash and recycling bins in waste management systems.”
Engineers also created simulation tools to design discs that produce specific ultrasonic tones when struck.
Early models identified approximately 1,300 viable designs, and testing used 15 of them to confirm performance.
Ultrasonic signals also remain localized, limiting the distance sound travels. Nearby microphones detect activity, while distant devices remain unaware, helping to keep the system private and focused on specific areas.
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