Ultrasonic noise, generally defined as sound above 20 kHz, is often assumed to be safe because most adults cannot hear it. That assumption is outdated and only partially true. Early occupational studies linked high-level ultrasonic exposure to headaches, nausea, fatigue, and temporary hearing shifts, and a growing body of research suggests the public is now being exposed to airborne ultrasound in everyday settings with little regulatory oversight. For pets, the picture is even more complicated: dogs and cats hear well into the ultrasonic range, making them far more susceptible to sounds their owners cannot detect.
Where Ultrasonic Noise Actually Comes From
Most people associate ultrasound with medical imaging or perhaps a pest-repeller plug-in, but the real list of sources is surprisingly long. In workplaces, low-frequency ultrasonic devices such as industrial washers, ultrasonic welders, drills, soldering tools, and galvanizing equipment are the primary culprits. Compressors, pneumatic tools, and high-speed machinery like planers, grinders, circular saws, and certain textile machines also generate ultrasound as a byproduct. Plasma-arc welding and air-acetylene welding add still more ultrasonic energy to the environment.1PubMed Central. Possible Effects on Health of Ultrasound Exposure, Risk Factors in the Work Environment and Occupational Safety
Outside the factory, consumer electronics are a growing source. Ultrasonic pest repellers are marketed in the millions. Anti-loitering devices emit high-frequency tones in public spaces. Even mundane equipment like LED lighting and ventilation systems can produce low-level ultrasonic emissions. Research in modern animal facilities found that standard fluorescent and LED lights generated ultrasonic noise between about 40 and 47 kHz at roughly 31 dB SPL, a level low enough to go unnoticed by human staff but well within the hearing range of laboratory rodents.2PubMed Central. Investigating audible and ultrasonic noise in modern animal facilities The implication is that ultrasonic noise in shared human-animal environments is more common than most people realize.
Reported Effects on Humans
People who live or work near ultrasonic sources have reported a cluster of symptoms: headaches, nausea, dizziness, tinnitus, fatigue, and a vague sense of pressure or discomfort. Early occupational research documented temporary hearing threshold shifts in workers exposed to high-intensity ultrasound, along with nausea, headache, fatigue, and migraine. These early findings were taken seriously enough to produce preliminary exposure limits, though the researchers who gathered the data considered their evidence base insufficient to finalize guidelines.3PubMed Central. Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?
More recent research has tried to sort out whether the symptoms are caused directly by ultrasound or by the expectation of being harmed. A double-blind provocation study exposed participants to inaudible 20-kHz ultrasound and found no evidence that the ultrasound itself provoked symptoms. There was, however, evidence of small nocebo effects, meaning people who expected to feel sick tended to report feeling sick regardless of whether the ultrasound was on. The researchers noted that their study did not reproduce the severe symptoms reported by some members of the public, and acknowledged that this might be because of the sound pressure level or duration used in the experiment, or the strength of the nocebo stimulus.4PubMed. Effects of very high-frequency sound and ultrasound on humans. Part II: A double-blind randomized provocation study of inaudible 20-kHz ultrasound
That result is worth reading carefully. It does not prove ultrasound is harmless. It shows that one particular exposure, at one frequency and one level over a short period, did not trigger the reported symptoms in a controlled setting. Real-world exposures often involve different frequencies, longer durations, higher intensities, or combinations with audible noise, and none of those variables were replicated in that study. The absence of evidence for harm in a single controlled trial is not the same as evidence of safety across all the situations people encounter.
Why Safety Guidelines Are Behind the Curve
One of the most striking findings in this area is how thin the regulatory framework is. A detailed review published in the Proceedings of the Royal Society concluded that the public is being exposed to airborne ultrasound without their knowledge, and that existing guidelines are insufficient for such exposures. The vast majority of current standards address only occupational exposure, where workers know they are being exposed, can be monitored, and can wear hearing protection. Public exposure, by contrast, happens in stores, transit stations, and private homes where none of those safeguards exist.3PubMed Central. Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?
The evidence base behind the guidelines themselves is another problem. Most of the foundational research was conducted over 40 years ago, by researchers who openly considered their data insufficient to set permanent limits. Those preliminary numbers were never formally upgraded with new data, yet they have been inherited by modern standards documents as if they were settled science. Meanwhile, consumer ultrasonic devices have proliferated, public environments have added more electronic equipment that incidentally emits ultrasound, and no systematic measurement campaign has mapped what levels the general public is actually experiencing.
Accurate measurement of airborne ultrasound is itself a technical challenge. The calibration of microphones for ultrasonic frequencies carries an expanded measurement uncertainty of about 0.3 to 0.7 dB in the range from 20 to 100 kHz, which sounds small but can matter when you are trying to decide whether a given environment exceeds a safety threshold.5PubMed. Uncertainty analysis on free-field reciprocity calibration of measurement microphones for airborne ultrasound On top of that, the spatial resolution required to capture an ultrasonic field accurately depends on both the scanning grid and the physical size of the microphone, and getting those parameters wrong can distort results meaningfully.6PubMed. Investigation of resolution and microphone size for measurements of airborne ultrasound In other words, even if regulators wanted to enforce limits on public ultrasonic exposure today, measuring compliance reliably would not be straightforward.
How Dogs and Cats Experience Ultrasound
For pets, the question of ultrasonic harm takes on a different character because they can hear what you cannot. Dogs are sensitive to frequencies well above the human ceiling of roughly 20 kHz. A study measuring canine hearing thresholds found that at 20 kHz, dogs had an average threshold of about 8.5 dB SPL, which was remarkably lower (meaning more sensitive) than previous estimates suggested.7PubMed Central. Determining Hearing Thresholds in Dogs Using the Staircase Method Many dogs can hear frequencies up to 45 kHz or higher. A pest repeller operating at 25 kHz is not just detectable to them; it may be loud and grating.
Cats have even broader hearing. Research has measured the domestic cat’s hearing range as extending from 48 Hz up to 85 kHz at moderate sound levels, giving cats one of the widest hearing ranges among mammals.8Hearing Research. Hearing range of the domestic cat That means a cat can perceive ultrasonic noise from sources that are not even close to the upper end of a dog’s range. If your home contains an ultrasonic pest deterrent, an electronic device with ultrasonic emissions, or even certain light fixtures producing ultrasound in the 40–50 kHz band, your cat is likely hearing it. Whether that sound is annoying, distressing, or damaging depends on its intensity and duration, but the point is that dismissing it as “silent” only applies to the human perspective.
The practical gap here is large. Pet owners buy ultrasonic pest repellers assuming they are inaudible to everyone in the household except rodents and insects. In reality, the devices broadcast a sound that dogs and cats perceive clearly, often at close range and for hours at a time. No regulatory body currently requires labeling these products with warnings about pet exposure, and no long-term studies have examined whether chronic low-level ultrasonic exposure causes hearing damage or behavioral changes in companion animals.
Pest Repellers and What They Actually Emit
The marketing for ultrasonic pest repellers typically emphasizes two things: that the sound drives away rodents or insects, and that it is completely inaudible and harmless to people. Research paints a less tidy picture. An investigation into the acoustical output of a commercial ultrasonic rodent repellent found that, alongside the expected high-frequency signals, the device produced a faint but audible sound in the 4–5 kHz range. On average, short-term exposure to the device did not cause significant adverse effects. But when the signal was perceptible, as it frequently was for younger participants at lower frequency settings and when two sources were emitting simultaneously, several people described it as disturbing.9PubMed. Assessment of short-term exposure to an ultrasonic rodent repellent device
This matters for two reasons. First, these devices do not emit a single clean ultrasonic tone; they can leak audible frequencies that younger people and children pick up. Second, the “no significant adverse effects” conclusion applies to short-term exposure in a study setting, not to the round-the-clock operation that pest repellers are designed for. A device plugged into a kitchen wall socket 24 hours a day creates a chronic exposure scenario that no human study has properly tested.
For pets living in the same room, the exposure is even more direct. Dogs and cats cannot leave a room to escape a sound the way a study participant can remove headphones. If a repeller is placed in a small space like a garage or utility room where a pet also spends time, the animal may be subjected to continuous high-frequency noise at close range with no ability to communicate discomfort in a way the owner recognizes.
Anti-Loitering Devices and Young People
A different class of ultrasonic device has raised ethical as well as health concerns. The Mosquito is an anti-loitering device that emits a high-frequency tone designed to be inaudible to most people over the age of about 25 but intolerable to younger ears. By exploiting age-related hearing loss, the device creates zones that are effectively inhospitable to young people. Although marketed as a benign tool for managing public space, critics have argued that the Mosquito causes pain and amounts to a weaponization of sound.10Canadian Journal of Communication. Silent Alarm: The Mosquito Youth Deterrent and the Politics of Frequency
The Mosquito typically operates at frequencies around 17 kHz, which is technically within the upper limit of audible sound rather than true ultrasound, but the principle is the same: high-frequency acoustic energy is used as a deterrent precisely because it causes discomfort to those who can hear it. Devices like this sit in a regulatory gray zone. They are not loud enough to trigger occupational noise standards. They are marketed for outdoor use where exposure is brief. But children and teenagers passing through the area have no choice in the matter, and repeated exposure for anyone who lives or works nearby could accumulate into something more than a momentary annoyance.
Who Is Most Vulnerable
The impact of ultrasonic and very high-frequency noise is not uniform across the population. Several groups face heightened risk.
Children and teenagers hear higher frequencies than adults do. The age-related loss of high-frequency sensitivity that makes adults oblivious to certain ultrasonic emissions has not yet occurred in young people. A device that an adult cannot detect may be plainly audible, and unpleasant, to a child in the same room. This is not a theoretical concern; the rodent repeller study cited earlier found that younger participants were the ones most likely to perceive the signals and describe them as disturbing.9PubMed. Assessment of short-term exposure to an ultrasonic rodent repellent device
People on the autism spectrum are another group that deserves specific attention. Hyperacusis, a condition in which ordinary sounds are perceived as uncomfortably or painfully loud, is highly prevalent among people with autism spectrum disorders. This auditory hypersensitivity can trigger strong aversive reactions that affect social participation and academic performance.11PubMed Central. Hyperacusis in Autism Spectrum Disorders For someone with hyperacusis, an ultrasonic emission that a neurotypical adult cannot hear, or can hear but tolerates easily, could be genuinely painful or disorienting. Placing ultrasonic devices in classrooms, shops, or public transit areas without considering this population creates an accessibility problem that rarely enters the conversation.
People with tinnitus may also be affected. While the relationship between ultrasonic exposure and tinnitus is not fully mapped, tinnitus often involves the perception of high-frequency sounds, and external high-frequency stimuli can interact with or exacerbate that perception. For someone already managing chronic tinnitus, adding an uncontrolled source of high-frequency acoustic energy to their environment could plausibly worsen their symptoms, even if the same source would be benign for someone without the condition.
Hidden Ultrasonic Noise in Animal Environments
Research into modern animal facilities has revealed a category of ultrasonic exposure that nobody planned for. Scientists investigating noise in laboratory animal housing discovered that common equipment generates significant ultrasonic output. Standard lighting in the facilities produced continuous ultrasonic noise between about 40 and 47 kHz. More strikingly, routine activities like handling metal equipment created intense broadband noise bursts. When forceps were dropped onto the base of a laminar airflow cabinet, the impact reached over 112 dB SPL across the full measured range and produced ultrasonic noise above 20 kHz at nearly 90 dB SPL, a jump of almost 50 dB above background levels.2PubMed Central. Investigating audible and ultrasonic noise in modern animal facilities
This finding has implications beyond the laboratory. If institutional-grade lighting and everyday metal-on-metal impacts create those ultrasonic levels, similar sources likely exist in homes, veterinary clinics, grooming facilities, and pet boarding operations. Your dog or cat may be experiencing ultrasonic noise from sources you would never suspect, and because you cannot hear it yourself, you have no cue that anything is wrong. Behavioral signs of distress in pets, such as restlessness, avoidance of certain rooms, excessive barking, or changes in appetite, could in some cases trace back to acoustic irritants that are inaudible to their owners.
Practical Steps for Reducing Exposure
Given the state of the evidence, a few common-sense measures can reduce ultrasonic exposure for both your household and your pets without requiring specialized equipment.
- Reconsider pest repellers: If you use ultrasonic pest deterrents and share your home with dogs, cats, or young children, recognize that those household members can almost certainly hear the device. Weigh the questionable pest-control benefit against the potential for chronic auditory irritation.
- Watch for pet behavior changes: If a pet begins avoiding a room, seems agitated, or develops unexplained behavioral shifts after new electronics are introduced, consider whether an ultrasonic emission might be the cause. Try unplugging the device and observing whether the behavior resolves.
- Keep children in mind: When selecting electronic equipment for shared family spaces, be aware that children hear higher frequencies than you do. A device that seems silent to an adult may not be silent to a six-year-old.
- Distance helps: Ultrasound attenuates in air more rapidly than lower-frequency sound. Keeping distance between people or pets and any suspected ultrasonic source reduces exposure meaningfully, even a few extra meters matter.
What Smartphone “Detectors” Can and Cannot Do
A number of smartphone apps claim to detect ultrasonic emissions. The appeal is obvious: if you suspect a device is emitting ultrasound, you want to confirm it without buying specialized equipment. The problem is that smartphone microphones are designed to capture the human voice, which peaks around 1–4 kHz. Most phone microphones roll off steeply above 15–18 kHz, meaning they physically cannot pick up true ultrasonic frequencies above 20 kHz. An app that claims to detect ultrasound on a standard phone is, at best, detecting audible high-frequency noise near the top of the phone’s range, and at worst, displaying meaningless artifacts.
Professional-grade measurement of airborne ultrasound requires quarter-inch condenser microphones calibrated specifically for the ultrasonic range, and even those instruments carry a measurement uncertainty of a fraction of a decibel that researchers work hard to characterize and minimize.5PubMed. Uncertainty analysis on free-field reciprocity calibration of measurement microphones for airborne ultrasound If you genuinely need to measure ultrasonic noise in your environment, an acoustics consultant with appropriate equipment is the reliable route. Smartphone readings in this frequency range should not be trusted for any practical decision.
Exotic and Small Pets at Particular Risk
Dogs and cats get most of the attention in discussions of pet-safe ultrasound, but they are not the most vulnerable animals in many households. Rodents, rabbits, ferrets, and birds often have hearing that extends deep into the ultrasonic range. Laboratory mice and rats, for instance, communicate extensively using ultrasonic vocalizations above 20 kHz. A pet hamster or guinea pig living near an ultrasonic pest repeller designed to target wild rodents is experiencing exactly the kind of sound the device was engineered to make aversive. The irony is not lost on veterinarians who field calls about small pets displaying stress behaviors after a repeller is installed.
Birds present a different profile. While most bird species do not hear as high as mammals, some species are sensitive to vibrations and pressure changes that accompany intense acoustic output even if the primary frequency is above their hearing range. The broader lesson is that any decision about ultrasonic devices in a home should account for the specific animals living there, not just assume that “pet safe” on a label applies to every species equally.