Yes, the bracelet was real—but it was a University of Chicago research prototype, not a magical consumer device that defeats every microphone. Its ring of ultrasonic transducers exploited a weakness in some commodity microphones, making captured speech difficult for speech-recognition systems to understand. The project was reported by Futurism on February 15, 2020; the university still describes the technology as a prototype rather than a normal retail product.
What the viral bracelet actually was
The device commonly called the “Bracelet of Silence” was developed by University of Chicago researchers including Yuxin Chen, Huiying Li, Shan-Yuan Teng, Steven Nagels, Zhijing Li, Pedro Lopes, Ben Y. Zhao and Haitao Zheng. Contemporary coverage made it look like a chunky cyberpunk cuff with roughly 24 small speakers. Technically, the final ring described in the project documentation used 23 ultrasonic transducers, with one position removed to accommodate the hinge.
This was an acoustic device, not a radio-frequency jammer, EMP or blocker for cellular, Wi-Fi or Bluetooth signals. It projected ultrasound toward nearby microphones while the wearer spoke.
Futurism’s February 15, 2020 report popularized the claim that the bracelet could jam “any spying microphones nearby.” The university’s project page and technical publications describe a narrower result: disruption of tested microphones under particular conditions.
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Prototype hardware
| Part | Documented specification |
|---|---|
| Form | Circular wearable ring in a 3D-printed enclosure |
| Transducers | 23 NU25C16T-1 ultrasonic transducers in the final ring; contemporary media described the concept as 24 speakers |
| Operating frequency | Approximately 25 kHz |
| Signal generator | AD9833 |
| Controller | ATmega32U4 microcontroller |
| Amplifier | PAM8403, rated at 3 watts in the technical description |
| Power | 3.7-volt, 500-mAh rechargeable lithium-polymer battery with a 3.7-to-5-volt step-up regulator |
| Ring size | About 9 centimetres outer diameter |
The dimensions and components come from the project’s technical documentation, including the University of Chicago dissertation record. They are engineering details of a research prototype, not a current product specification.
How ultrasonic microphone jamming works
The bracelet emits high-frequency sound intended to sit above the normal range of human hearing. Many inexpensive microphone assemblies are not perfectly linear: a sufficiently strong ultrasonic signal can interact with the microphone’s electronics and produce interference at audible frequencies inside the recording chain.
In plain terms, the microphone can record a loud, static-like or distorted signal alongside the speaker’s voice. The person in the room may hear little or nothing, while the microphone receives corrupted audio. The technique attacks the microphone during capture; it does not erase a clean recording afterward.
The underlying mechanism is described in the project materials and the research paper at arXiv. “Ultrasonic” does not mean universally harmless or inaudible: hearing sensitivity varies, and animals or nearby equipment may respond differently.
Why make it a bracelet?
A conventional ultrasonic jammer can be directional. Its transducers may create dead zones, and a stationary unit generally has to be aimed at the target microphone. The ring places emitters around the wearer’s arm, while ordinary hand movement changes their position and orientation during conversation.
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The project page reports that the wearable design outperformed tested stationary jammers in coverage and maintained more than 87% jamming effectiveness across the tested angle range. That is the researchers’ result under their test conditions, not a guaranteed spherical privacy field. Distance, orientation, room reflections, microphone construction and the relative position of the speaker and recorder still matter.
What the experiments demonstrated
The researchers evaluated visible microphones, concealed microphones and microphones covered by materials such as cloth or paper. They measured speech-recognition performance and compared the wearable ring with planar or stationary jammers. The project page says the wearable could disrupt acoustically reachable microphones even when those microphones were hidden or covered in the tested scenarios.
Recording is not the same as transcription
The important metric was word error rate (WER), the percentage of words a speech-recognition system misidentifies. A high WER means that a particular automated transcript is unreliable. It does not prove that no waveform was stored, that a human could not understand any fragment, or that a more capable processing system would fail.
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- Recording: whether sound reached storage at all.
- Audibility: whether a person can understand the resulting audio.
- Speech recognition: whether a chosen model can transcribe it accurately.
- Privacy: whether useful information such as names, keywords, identity or emotion remains recoverable.
Those are different outcomes. The bracelet’s strongest demonstrated benefit was degrading microphone capture and automated speech recognition, not proving that every form of audio analysis becomes impossible.
Does it block Alexa, Siri or a hidden recorder?
It targets the acoustic input path—the microphone—not the assistant, operating system or network. A susceptible microphone used by a smart speaker, phone or voice assistant could be affected, but the bracelet does not shut down Alexa, Siri or Google Assistant, disconnect a device, or prevent processing through another microphone.
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“Hidden microphone” means a microphone that was concealed or covered in the tested setup, yet still acoustically reachable. It does not mean every covert recorder regardless of distance, shielding, microphone design or placement.
- It cannot stop a camera, lip-reading or visual surveillance.
- It cannot undo audio that was recorded before the jammer was activated.
- It cannot protect against a second recorder positioned outside the effective field.
- It may affect only some microphones in a device with multiple microphones.
Where the claim fails
The word any is the major exaggeration. The evidence supports disruption of tested commodity microphones, not universal defeat of every recording system.
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- Distance: ultrasonic intensity falls as the microphone gets farther away.
- Position and shielding: a microphone behind a thick enclosure, wall or acoustically isolated membrane may receive too little energy.
- Signal processing: filtering or other processing may reduce the injected interference.
- Speech leakage: failed transcription does not guarantee that no intelligible fragments or metadata remain.
- Power and comfort: a wearable amplifier and transducer array consume battery power and can create heat and bulk.
- Collateral effects: the device may ruin a legitimate phone call, video, interview, accessibility microphone or personal recording.
- Human and animal hearing: the intended signal is largely inaudible to ordinary listeners, but hearing varies and animals may perceive frequencies people do not.
An anecdotal discussion has questioned compatibility with newer iPhones and their microphone membranes; that is an unverified user report, not a published performance result. See the discussion at Hacker News only as anecdotal context.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Can you buy the original bracelet?
There is no verified evidence that the University of Chicago bracelet became a mainstream consumer product. The university’s technology-transfer listing identifies it as a prototype and seeks licensing, investment and co-development opportunities: official technology-transfer page.
Reports that it would cost “about $20” refer to an estimated manufacturing cost quoted in 2020-era coverage. That figure is not a current retail price, a complete bill of materials or a promise that a finished bracelet can be bought for $20.
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Can a technically capable maker build one?
The team published MATLAB simulation code, Arduino firmware and 3D-printing files. The project page links to the open-source repository, which is intended to support reproduction of the simulations, hardware design and prototype.
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That documentation does not make assembly plug-and-play. A builder would need suitable ultrasonic transducers, a signal generator, microcontroller, amplifier, battery and regulator, plus a custom enclosure and a way to measure whether the actual target microphone is being disrupted. Safe electrical construction and acoustic testing are essential. The published materials do not establish guaranteed performance with modern phones, smart speakers or every recording system.
Is an ultrasonic microphone jammer legal?
Do not automatically apply the law for radio jammers to this device. FCC enforcement notices clearly address unauthorized radio-frequency jammers that interfere with cellular, GPS, Wi-Fi and similar communications. See the FCC materials at DA-20-1465A1 and DA-14-1785A1.
The University of Chicago bracelet is described as an acoustic ultrasonic microphone jammer, not an RF communications jammer. Those FCC notices do not, by themselves, settle every legal question about an acoustic device. Noise limits, product safety, privacy and recording-consent laws, workplace or school rules, accessibility, harassment and interference with other equipment may still matter. Anyone considering use in a workplace, court, aircraft, school or public venue should obtain advice for the relevant jurisdiction.
What to check before considering any microphone jammer
- Define the target: speech capture is different from blocking cellular or Wi-Fi communications.
- Measure the required range: a wearable intended to protect one conversation is not a room-scale solution.
- Identify the microphones: test the actual phone, speaker, recorder or conference system involved.
- Set the privacy objective: transcript corruption is not the same as eliminating every recoverable audio signal.
- Assess collateral damage: nearby legitimate recording and accessibility equipment may also fail.
- Verify rather than trust advertising: vendor “range” claims are not interchangeable with peer-reviewed speech-recognition tests.
- Check local rules: venue, employer, school, transportation, recording-consent and noise requirements may prohibit use.
More predictable privacy measures
For most people, basic controls are more reliable than an unvalidated jammer:
- Unplug or disable smart speakers before sensitive conversations.
- Use a hardware microphone-mute switch where the device provides one.
- Keep private discussions away from unnecessary phones, cameras and voice assistants.
- Review microphone permissions, cloud-retention settings and account access.
- Use a known secure meeting space and make sure legitimate participants understand the recording setup.
Verdict
The cyberpunk bracelet was a genuine and inventive 2020 research prototype. Its ultrasonic ring exploited nonlinear behavior in some commodity microphones and showed strong disruption under tested conditions, including concealed or covered microphones. But it was never established as a universal anti-spying shield, a device that disables Alexa or Siri, or a normal retail product. Treat “jams any microphone nearby” as a simplified headline for a conditional microphone-capture attack—not as a guarantee against every recorder.
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