Yes, several real technologies can make a person hear sounds or voices that nobody around them can hear. These range from commercially available speakers used in museums and stores to military-grade acoustic devices and even laboratory-demonstrated microwave effects. Understanding what these devices actually do, and what they can’t do, helps separate fact from fiction.
Directional Speakers: Sound Only You Can Hear
The most common and widely available technology is the directional speaker. Companies like Holosonics manufacture a product called the Audio Spotlight, which creates a tight beam of sound using ultrasound waves. If you step into the beam, you hear audio clearly. Step a few feet to the side, and it’s silent. The company claims its speakers produce sound ten times more isolated than any conventional speaker on the market.
These devices are already installed in thousands of public spaces. Museums use them so visitors hear narration only when standing in front of a specific exhibit. Banks use them for privacy at teller windows. Retailers use them to play advertisements that reach only the person standing near a display. Libraries, hospitals, trade shows, and digital signage companies all use directional audio for the same reason: delivering sound to one spot without disturbing anyone nearby.
If you’ve ever walked through a store and suddenly heard a voice or music that seemed to come from nowhere, then lost it after a few steps, you likely passed through a directional speaker beam. The experience can feel startling if you don’t know the technology exists, but it’s a straightforward acoustic effect with no health risks.
Bone Conduction Devices
Bone conduction technology bypasses your outer ear entirely. Instead of pushing sound waves through the air into your ear canal, these devices press a small vibrating transducer against your skull. The vibrations travel through bone and reach your inner ear directly, where they’re processed as sound.
The technology works through at least five different pathways. Some vibrations travel through the skull bone itself. Others generate sound pressure inside the ear canal from the inside out. Placing a bone conduction transducer near the ear canal opening improves sensitivity by roughly 20 decibels compared to placing it on the bony bump behind your ear (the mastoid), and at certain frequencies the improvement reaches 40 decibels.
Consumer bone conduction headphones are widely sold for exercise and accessibility. Because they leave your ears open, you can hear both the audio and your surroundings. For someone watching you, though, there’s no visible earbud or speaker. The sound exists only for the wearer. Military and law enforcement also use bone conduction communicators built into helmets, allowing personnel to receive voice transmissions without any external audio leaking out.
Long Range Acoustic Devices
Long Range Acoustic Devices, commonly called LRADs, are powerful directional speakers originally designed for the military and now used by police departments and emergency services. Unlike the quiet, subtle directional speakers in museums, LRADs are built to project voice commands or alarm tones over long distances with extreme clarity.
The smaller LRAD 100x operates between 0 and 137 decibels. The larger LRAD 450x reaches up to 146 decibels, which is louder than a jet engine at close range. At their lower “green zone” settings (under 105 to 114 decibels depending on the model), they function as powerful megaphones for announcements. At higher settings, they can cause pain and potential hearing damage, which is why police departments require minimum distances of 200 to 650 feet when using the loudest modes.
LRADs are used during emergency management, rescue operations, crowd control, and tactical situations like barricaded suspects. Their tight beam means the sound is loudest for the person or group directly in front of the device, while people off to the side hear much less. If you were targeted by an LRAD, you’d have no doubt something external was happening. These are not subtle or covert.
The Microwave Auditory Effect
The most unusual technology in this category is the microwave auditory effect, sometimes called the Frey effect after the researcher who first documented it in the 1960s. When a pulse of radiofrequency energy hits your head, it causes a tiny, rapid thermal expansion in brain tissue. That expansion generates an acoustic wave inside your skull. The wave bounces off the interior of the skull, exciting natural resonance modes at around 7 to 10 kilohertz in adults, and propagates to the inner ear through bone conduction.
The result is a perceived click, buzz, or tone that has no external sound source. The sound is generated inside your own head by the interaction between microwave energy and tissue. This effect has been reliably demonstrated in laboratory settings and is well understood physically. It works through the same thermoacoustic principle used in some medical imaging techniques.
Whether this effect could be scaled into a practical device that transmits intelligible speech remains debated. Generating simple clicks or buzzing with pulsed microwaves is proven. Encoding complex voice information into those pulses at safe energy levels is a different engineering challenge, and no publicly confirmed device has demonstrated this capability. The Frey effect gained renewed public attention during investigations into unexplained health symptoms reported by U.S. diplomats abroad, though those cases remain unresolved.
How These Differ From Auditory Hallucinations
People searching this topic sometimes wonder whether what they’re hearing could be coming from a device or from their own brain. The distinction matters, and there are real differences between the two experiences.
Auditory hallucinations, most commonly associated with conditions like schizophrenia, can be perceived as coming from an external location or from inside the head. Research on patients with schizophrenia found that those who perceived voices as internal (originating inside the head) were more likely to recognize the voices as self-generated. Those who perceived voices as external were less likely to have that insight. Hallucinated voices also tend to have personal content: they may comment on your behavior, address you by name, or say things connected to your emotions and memories.
Sound from an external device, by contrast, has consistent physical properties. It gets louder or quieter as you move. It stops when you leave a location. Other people with recording equipment can detect it. It doesn’t respond to your thoughts or contain personally meaningful content. If you’re hearing sounds that follow you across different locations, that change based on your emotional state, or that only you can hear regardless of environment, those characteristics point toward an internal origin rather than a technological one.
What’s Commercially Available Today
Directional speakers and bone conduction headphones are the two technologies you can actually buy. Directional speakers from companies like Holosonics are sold to businesses and institutions, not typically to individual consumers, though smaller parametric speaker kits exist for hobbyists. Bone conduction headphones are widely available from brands like Shokz and cost roughly the same as conventional wireless earbuds.
LRADs are restricted to military, law enforcement, and maritime use. Microwave auditory devices do not exist as consumer or commercial products. The underlying physics is real, but no device on the market uses microwave pulses to transmit audio to a person’s head. Any claim that such a device is being used covertly against individuals should be evaluated with significant skepticism, given the energy levels and equipment that would be required.