برچسب: Dogs

I Found Ultrasound in My (Dog’s) Home
Four speeds, from slow to fast, of an Andis rotary tool for nail grinding

People in the dog community are worried that sounds we can’t hear might be bothering our dogs. But we can’t check for ultrasound with consumer equipment, even smartphones, because consumer microphones don’t detect sound above 20,000 cycles per second (20,000 Hz). They have no reason to, since we can’t hear in that range. But dogs can. They hear up to 45,000 Hz or higher.

My Search for Ultrasound

In 2023, I bought an ultrasound microphone and learned how to interface it with my equipment. In January 2024, I published a post with instructions on how to check your home and environment for ultrasound that your dogs might be able to hear. I found that many ordinary noises had an ultrasound component—things like clickers, keyboard strokes, motors, even barking dogs. But I was looking for duration or intermittent ultrasound that might be generated by electronic devices and didn’t have a component audible to humans.

I didn’t find any for a while, but I kept searching. You can see my list of items that didn’t emit detectable ultrasound below.

I recently checked the sound environment again, and found some constant, low-level, electronics-generated ultrasound in dogs’ hearing range that was not accompanied with anything in the human hearing range.

The culprits: three adapters that put out ultrasound, but no sound audible to humans

I found what people have been worried about: sound that dogs can hear but we can’t. But the sound was very quiet; it would likely be inaudible unless a dog was very close.

This ultrasonic noise was emanating from ordinary AC/DC adapters. I have at least 20 of these in my house. I found three that put out a high-frequency noise that was outside of humans’ hearing range. These were the adapters for:
- A floor lamp with a 24 V DC power supply. It put out a group of frequencies peaking around 21,000, 31,000, and 43,000 Hz.
- A decorative “Moon” lamp with a 12 V DC power supply. It put out a group of frequencies peaking around 23,000, 28,000, and 33,000 Hz. This adapter even put out a little sound when the lamp was off, but more when it was on.
- A Fi GPS collar charger that output 5 V DC. The USB adapter put out a band of frequencies peaking around 22,000, 30,000, and 45,000 Hz.
Note that it was the adapters, not the lights or the charger putting out the sound. I spent a lot of time pointing my microphone at the wrong ends of things!

The following image shows the ultrasound put out by the adapter of the floor lamp. The x axis is time and the y axis is frequency. You can see blue and green bands in the 20–70 kHz range that correspond to the peaks I listed above during the periods the lamp is on. Also note that there is no change in the sound output lower than 20 kHz when the lamp is on. That means that we humans can’t hear the adapter. (The thin vertical lines were created by the click of the remote for turning the lamp on and off.) For more information on reading this kind of diagram, see the page of examples that accompanies this post.

I found one more item that had a constant, quiet, high-frequency sound in the human hearing range plus sounds in the ultrasound range. These sounds were coming from a battery charger for a Dremel tool (8220). It put out an audible tone at 6,000 Hz, and harmonics (mathematically related higher tones) at 12,000, 18,000, and 24,000 Hz. The charger itself (the part where you insert the battery, in this case not the wall plug) has a built-in AC/DC adapter.

AC/DC Adapters

AC/DC adapters function as power supplies for devices that use direct current and lower voltage than what our wall outlets provide. They are the things that often annoy us by taking up more than one space on a power strip. They are often referred to as wall warts because of their bulk. That makes them easy to locate in your home. Two of my culprits were wall warts, and one had a profile almost as small as a normal AC plug.

What Do They Sound Like and How Audible Are They to Dogs?

Here are recordings of the sounds, digitally altered to make them audible to humans. There is some unavoidable distortion, but you can get the general idea. To create these sounds, I did the following:
1. I recorded the sound in WAV format using my Dodotronic 192 kHz ultrasound mic attached to my iPhone 12 Mini using the free Ultrasonic Analyzer app.
2. I imported the audio file into the free sound software Audacity on my Mac.
3. I applied a high-pass filter to isolate the ultrasound.
4. I amplified the signal. The sound was so quiet that I needed to amplify it to be able to see on the screen where the device was on and where it was off so I could edit. See this image.
5. I changed the pitch to bring it down to human hearing range.
6. Sometimes I amplified again.
7. I exported the file as an MP3. The limitations of MP3s don’t affect the sound quality needed for these recordings.
Floor Lamp

“Moon” Lamp

Fi Collar Charger Plug

The moon lamp’s power adapter puts out extremely quiet ultrasound even when the lamp is off

All the original sounds have ultrasound components in dogs’ hearing range, between 20,000 and 45,000 Hz. But the adapted versions are amplified in the above recordings; in all cases, the original sounds were much, much quieter.

For those of us who are concerned about them possibly bothering dogs, there is a blessing. Ultrasound waves are tiny. For instance, the wave that corresponds to the frequency of 25,000 Hz is 14 millimeters, or a little more than half an inch long. For comparison, a 60 Hz wave such as we could hear in a thunderstorm is 5.7 meters or almost 19 feet long. The tiny ultrasound waves don’t travel far over distances because they are reflected and absorbed so easily. It’s a good bet that even dogs don’t hear sounds such as the ones I presented above unless they are close to the source. The sounds are not blasting through whole rooms.

The two lamps are within about 2 meters of where Lewis sleeps on my bed. While recording, I moved the ultrasound mic from the lamp’s power adapter toward where Lewis sleeps. The mic stopped being able to pick up the sound at about 1 meter. You can see the attenuation of the sound as I moved the mic in this image.

Items I Tested with Null Results

Various scholarly and lay articles include lists of household devices that may put out ultrasound. I chose the following devices from those sources, tested, and detected no ultrasound. Other brands or models of these items might yield different results. Note that some of these items have been reported to scare dogs (Grigg et al., 2021). But noises do not have to have an ultrasound component to do so, and we don’t know if the ultrasound component contributed to the fear response.
- new and old lights: fluorescent, incandescent, LED including ring lights, night lights (which include adapters)
- screens: desktop computer, tablets, laptops, flat-screen TV
- motion-sensitive wildlife camera (Meek et al., 2014)
- laptop fan
- computer power adapters (I was sure I’d find a culprit here, but no. The Apple devices were all silent.)
- power strips
- USB wall plugs (these are also AC/DC adapters). The only noisy one was the Fi collar plug.
- smart plugs (two brands)
- refrigerator, microwave, oven
- smoke alarms on standby (not beeping)
- remote controls (except for occasionally the click of a key)
- ultrasonic humidifier
- space heater
- various fans
A Special Note about Smart Plugs

Because of a viral social media post from November 2023, many people are concerned about the possibility of so-called “smart plugs” putting out ultrasound. While it is possible, neither of the two I tested put out any. I deliberately chose cheap ones, because they are less likely to have strong quality control. An engineer pointed out to me that standard QC includes making sure electronics don’t put out noises such as coil whine or capacitor squeal in the human hearing range. But there is far less concern about the ultrasound range, for the same usual reason. We can’t hear it.

Note that smart plugs are not AC adapters. You might plug an adapter into one, though. Many smart plugs note 2.4 GHz or 5 GHz on the back. Don’t worry; these numbers refer to compatible Wi-Fi types and are not audible sound frequencies to humans or dogs.

Items That Produce Sound That Includes Ultrasound

These are not the stealth items that people are worried about, but I was fascinated to find so many noisy items that included ultrasonic frequencies. I created a page of ultrasound examples that includes images of the output of some of these loud items.

I had on a mask and a face guard, but ear protection would have been a good idea when using a rotary hammer drill as well!
- computer keyboard strokes
- clicker
- ultrasonic squeaker toy
- regular squeaker toy (you can see an image of the ultrasound components of noise from the preceding four items here)
- barks and whines of a small dog (Sibiryakova et al., 2021)
- clicks of various switches (like on remotes to fans or lamps)
- smoke alarms doing a test beep
- computer mouse clicks
- hands clapping
- jingling keys
- hand-held hair dryer
- jingling dog tags
- upright vacuum
- small rotary tools (e.g. Dremel)
- Makita screwdriver and drill
- Makita rotary hammer drill
For some of these items, the ultrasound component was among the loudest of the frequency bands. Because dogs’ hearing is more sensitive in the upper frequencies than ours, if a dog were close to such an item, they would likely hear a louder sound than we do. Most apps that measure volume, such as SPL meters for smartphones, don’t include the ultrasound range.

People frequently ask me about using ear-muff type ear protection for dogs who are fearful of thunder or fireworks. I always explain that such gear can’t protect against the huge sound waves generated by those low-frequency sounds. But these ear protectors can usually prevent the transmission of smaller sound waves very well. If your dog has been conditioned to wear ear gear, it would be a kindness to have them wear it as much as possible for grooming. The hair dryer and rotary tools I checked were loud in the ultrasound range, on top of being loud in high frequencies humans and dogs can both hear. Clippers may also put out ultrasound, but I didn’t have any to test.

“Ultrasound” Is an Arbitrary Definition

It’s crucial to understand that sound doesn’t magically change when the frequency goes over 20,000 Hz. That boundary of 20,000 Hz for ultrasound is derived from “sound that is too high for humans to hear.” It’s a handy distinction, but it’s based on biology, not physics. It’s anthropocentric. Ultrasound is just sound with a higher frequency. I always make the point in my sound webinars that we shouldn’t assume that a sound is aversive to dogs if it is in the ultrasound range, even though there are some oddball online articles that claim this is so. Keep in mind that dogs’ hearing evolved to function in that range. Many small animals that are prey to canids vocalize in that range. It’s no coincidence that domestic cats can hear in that range and even higher, too.

Anything happening above 20,000 Hz is a mystery to us. But it’s not to dogs; it’s just part of their world. It is quite possible that a constant noise in the ultrasound range could bother some dogs. It’s also likely that many dogs habituate to it, just as many dogs (and many humans) stop noticing other ongoing stimuli. For instance, the furnace is on in my house as I write this. There is the sound of the fan blowing air through the ductwork and perhaps the sound of the furnace itself coming through the registers. But I don’t “hear” these long duration sounds unless I turn my attention to them. Likewise, most of us who live in cities don’t notice the common 60-Hz hum of transformers. But people who live in rural areas may notice it when they come to town. And some people are immediately bothered by some ongoing sounds or never habituate.

I have an example in another post of dogs hanging around during a very obnoxious ongoing sound, even deliberately basking in the sun close to the sound source. This example “proves” nothing about how all dogs respond to sounds. However, it provides evidence that we may not be able to predict their response.

Limitations of My Testing

In the interest of transparency, I have created a separate page that delineates aspects of my home setup that affect the precision and accuracy of my data, in this and other posts that present results. I do not have controlled laboratory conditions. But I include in the list how the limitations were mitigated and why I can be confident in the results I have presented here.

Conclusion

Two major takeaways:
- The “stealth” sounds I found are likely inaudible unless a dog approaches close. Here is a photo of sound-reactive Lewis standing right next to the adapter for the floor lamp while he determines whether I have “webinar or Zoom treats” in a drawer.
- The ultrasound generated by motors can be loud. Properly conditioned hearing protection would be beneficial for dogs undergoing grooming procedures where a hair dryer or rotary tool is used.
Others have found more stealth ultrasound than I have, as described in this dramatically-titled CNET article. However, the author doesn’t discuss the rapid attenuation over distance of ultrasound, nor do they give us a good sense of how loud the sounds are.

I will keep performing periodic sweeps for ultrasound culprits in my area and report any findings.

Supplemental Materials

There are two pages with information relevant to this post:

Copyright 2025 Eileen Anderson

References

Grigg, E. K., Chou, J., Parker, E., Gatesy-Davis, A., Clarkson, S. T., & Hart, L. A. (2021). Stress-related behaviors in companion dogs exposed to common household noises, and owners’ interpretations of their dogs’ behaviors. Frontiers in veterinary science, 8, 760845.

Meek, P. D., Ballard, G. A., Fleming, P. J., Schaefer, M., Williams, W., & Falzon, G. (2014). Camera traps can be heard and seen by animals. PloS one, 9(10), e110832.

Sibiryakova, O. V., Volodin, I. A., & Volodina, E. V. (2021). Polyphony of domestic dog whines and vocal cues to body size. Current Zoology, 67(2), 165-176.

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12/04/2025
Evidence Suggests Dogs Prefer Free Food to Contrafreeloading
There is no experimental evidence to support the claim that dogs prefer to work for their food. In fact, there is evidence that they don’t.

Contrafreeloading is the behavior shown when an animal prefers to work for food (“earned food”) rather than take identical food that is freely available from another, nearby source (“free food”). — Inglis, 2022

A recent study found that statistically, the group of dogs they tested did not prefer contrafreeloading. They were willing to do it. I’ll discuss the results of the study below, including their definitions of “prefer” and “willing.”

But it’s just as important to learn about contrafreeloading findings in general. Studies on contrafreeloading have been done with many species. The studies have had large variability in results (Lentz & Cohen, 1980). Contrafreeloading is far from a universal preference; it appears more to be situational. And the many studies have yielded patterns that can inform us of situations in which this interesting phenomenon is more or less likely to happen.

Maned wolves have been observed to contrafreeload

Highlights of the Research

The seminal Jensen study (1963) is often cited to support contrafreeloading generally, including in dogs. In that study, rats preferred to press a bar to get food rather than eat it out of a dish. What many people miss are the full results of the study and the experimental follow-ups. Jensen’s rats contrafreeloaded in proportion to their reinforcement history with bar pressing—they worked for food more when they had built a habit. In 1972, Taylor performed an experiment similar to Jensen’s, but the rats in his study showed a strong preference for the free food, and an even stronger preference for free water. Taylor had more preference tests after the initial bar pressing training (Jensen had only one preference test), and contrafreeloading decreased over those sessions as time passed from the initial training. Lentz and Cohen (1980) worked with pigeons to investigate whether previous training with the contrafreeloading method of obtaining food had an effect. They also found that response rates in the presence of free food increased as a function of previous training.

“The data suggest that amount of training affects contrafreeloading and that this variable may be partly responsible for the large variability in responding observed among studies examining responding in the presence of free food.” — Lentz & Cohen, 1980, p. 48

The research continued, and scientists discovered many other factors that could influence whether animals chose to contrafreeload. A review paper in 1997 (Inglis et al.) compiled from previous studies seven items that could increase or decrease contrafreeloading . They used them to create a fuzzy logic model of contrafreeloading. Here are the seven items they considered. Supporting references for each of these are in the Inglis paper.
- Prior training. A reinforcement history with the method of accessing the food increases contrafreeloading.
- Deprivation level. This has both increased and decreased contrafreeloading in studies, depending on other variables.
- Effort required. The larger the effort needed to access the food, the less likely animals are to contrafreeload.
- Stimulus change. A change in the environment that correlates with the presentation of the earned food increases contrafreeloading. This might be a light or a sound. (Hmm, clicker training, anyone?)
- Environmental uncertainty. Novelty, ambiguity, and surprisingness increase contrafreeloading. For instance, animals are more likely to contrafreeload if that food source appears at an unpredictable location.
- Rearing conditions. Being reared under conditions of sensory deprivation increases contrafreeloading.
- Manipulation of the environment. Being able to control the environment may be a factor that increases contrafreeloading.
Red junglefowl, the primary precursor species to the domestic chicken, contrafreeload more than chickens (Lindqvist et al, 2002)

The list above comprises factors that can affect whether animals contrafreeload in different situations. But they do not explain why. One well-supported hypothesis is that the food itself is not the only reinforcer for food seeking behavior and eating. This “information hypothesis” notes that animals gain information about their environment when they contrafreeload. Such information could be helpful when seeking food in the future. This hypothesis has been borne out in studies.

An earlier review (Osborne, 1977) looked at contrafreeloading experiments through a behavior analysis lens and analyzed the reinforcement schedules identified in the studies. Osborne was apparently the first to note the effects of “stimulus change,” one factor listed above. After reviewing the research up to that point, Osborne states, ” . . . when the consequences of responding for food or obtaining it freely are made equally reinforcing (e.g., by equating stimulus change conditions for both alternatives), animals show a near exclusive preference for obtaining their food freely.”

Scientists have noted one other trend that supports the information hypothesis: domestic species tend to contrafreeload less. This is thought to be because their needs are taken care of by humans, and they don’t have a pressing need to seek information as wild animals do.

The Dog Study

The study of contrafreeloading in dogs (Rothkoff et al., 2024) is freely available online and very readable. Since the results were that dogs were “willing” to contrafreeload but didn’t “prefer” it, it’s important to learn how the scientists defined these terms.

Here’s how the experiment was set up. There were four “acclimation” sessions where the dogs gained experience with eating from a snuffle mat and became familiar with a setup of a snuffle mat and a tray of “free” food. After the acclimation sessions, there were 10 experimental sessions. In these sessions, half of the dogs’ meal was in the snuffle mat, and half in the tray of food. All acclimation and experimental sessions were video recorded.

A preference for contrafreeloading was determined by measuring how often the dog went to the snuffle mat first. A willingness to contrafreeload was determined by measuring how often the dog approached and interacted with the snuffle mat before finishing the food in the tray.

Results under these definitions were:

Preference. Only one of 38 dogs preferred to contrafreeload, going first to the snuffle mat 80% of the time. Twenty-two dogs went first to the tray for a large majority of the time, and fifteen dogs did not show a strong preference.

Willingness. Thirty of 38 dogs were “willing” to contrafreeload. Eight were not willing.

We can consider the characteristics of snuffle mats in view of Inglis et al.’s seven factors affecting contrafreeloading. Compared to many food-based enrichment toys for dogs, snuffle mats are low effort. They do not require the skill of puzzle feeders or frozen Kongs. I find it interesting that even with a comparatively easy “earned food” opportunity, most dogs preferred the free food. But mats also lack a stimulus change—there is no bell or click when the dog grabs a piece of food from the mat. That absence could make contrafreeloading less reinforcing.

There are two other interesting findings in the study: dogs’ activity level did not correlate with a preference for free food or contrafreeloading, but dogs with higher body condition scores (more overweight) were more likely to contrafreeload.

Finally, there is a thoughtful listing of the limitations of the study at the end of the writeup.

Enrichment

Where does this leave us with enrichment? In dozens of online articles on enrichment for dogs, you will see contrafreeloading referenced. You will see such absolute and non-evidence-based statements as:
- Dogs have a behavioral drive to earn their keep
- All dogs are contrafreeloaders
- Dogs will work for their food while passing up the same food for free
- Dogs would rather work for their food than not
The message is sometimes more nuanced, especially in the last couple of years. But you can still find plenty of articles that present contrafreeloading as an unquestioned attribute of dogs. Moreover, contrafreeloading is presented as a justification for enrichment activities that involve dogs working for food.

There are many enriching activities that don’t involve food toys

How this information about dogs and contrafreeloading might affect our enrichment choices is beyond the scope of this post. But here are some resources.

I have written about assessing whether a dog really enjoys a food toy, rather than assuming they do because they are “supposed to.”

Linda Case at The Science Dog has a comprehensive blog post about studies that assess whether food toys have beneficial qualities for dogs.

And here are three studies that might inform our choices about enrichment. The Breakfast Effect study (Miller & Bender, 2012) showed evidence that dogs, just like people, probably learn better when their stomachs are not empty. The Eureka Effect study (McGowan et al., 2014) provided evidence that solving problems can make dogs feel good. Finally, a fascinating paper in 2024 (Veissier et al.) suggested that opportunities for animals to gain information should be central to designing enrichment activities. This paper has a wealth of information that can help us think about enrichment in new ways.

A Personal Note

I use food toys. This study and the rest of the contrafreeloading research do not discourage me from offering them in moderation. Here are some things I do and don’t do with food toys.
- I do use food toys with dogs with cognitive dysfunction (easy ones).
- I do look for toys and activities where the dog’s enthusiasm seems much greater than the value of the food involved, as in searching games.
- I do use food toys with easy-to-access, high-value food for delay counterconditioning or just to sweeten difficult situations.
- I do help my dogs with those last stubborn pieces at the end if they ask me to.
- I don’t give a dog a challenging food toy on an empty stomach, nor do I train in that situation.
- I don’t ask a dog to work for food when they are sick or have a low appetite.
- I don’t ask a dog to work for food in a way that stresses them out. For instance, treat scatters can stress some intense resource guarders. Similarly, I don’t do food chase games with dogs who gulp it frantically.
- I don’t ask a dog to interact with a toy they find un-fun. Lewis has told me he finds Kongs, especially frozen ones, pretty “meh.” I give him Westpaw toys instead.
The research with dogs is only one study, with identified limitations. More research needs to be done. But with the power of the rest of the research behind it, the study is compelling. Scientists have been studying the “when” and the “why” of contrafreeloading for decades. It’s time for us to consider those findings in the dog training world.

Copyright 2025 Eileen Anderson

Related Posts

References
- Inglis, I. R., Forkman, B., & Lazarus, J. (1997). Free food or earned food? A review and fuzzy model of contrafreeloading. Animal behaviour, 53(6), 1171-1191.
- Inglis, I. R. (2022). Contrafreeloading. In Encyclopedia of Animal Cognition and Behavior (pp. 1665-1670). Cham: Springer International Publishing.
- Jensen, G. D. (1963). Preference for bar pressing over “freeloading” as a function of number of rewarded presses. Journal of Experimental Psychology, 65(5), 451.
- Lentz, B. E., & Cohen, S. L. (1980). The effect of prior training on the contrafreeloading phenomenon. Bulletin of the Psychonomic Society, 15(1), 48-50.
- Lindqvist, C., Schütz, K., & Jensen, P. (2002). Red jungle fowl have more contrafreeloading than white leghorn layers: Effect of food deprivation and consequences for information gain. Behaviour, 139(9), 1195-1209.
- McGowan, R. T., Rehn, T., Norling, Y., & Keeling, L. J. (2014). Positive affect and learning: exploring the “Eureka Effect” in dogs. Animal cognition, 17, 577-587.
- Miller, H. C., & Bender, C. (2012). The breakfast effect: Dogs (Canis familiaris) search more accurately when they are less hungry. Behavioural processes, 91(3), 313-317.
- Osborne, S. R. (1977). The free food (contrafreeloading) phenomenon: A review and analysis. Animal Learning & Behavior, 5(3), 221-235.
- Rothkoff, L., Feng, L., & Byosiere, S. E. (2024). Domestic pet dogs (Canis lupus familiaris) do not show a preference to contrafreeload, but are willing. Scientific Reports, 14(1), 1314.
- Taylor, G. T. (1972). A limitation of the contrafreeloading phenomenon. Psychonomic Science, 29(3), 173-174.
- Veissier, I., Lesimple, C., Brunet, V., Aubé, L., & Botreau, R. (2024). Rethinking environmental enrichment as providing opportunities to acquire information. animal, 101251.
Copyright 2025 Eileen Anderson

Image Credits
- Maned wolf from Wikimedia Commons, user Jonathan Wilkins , under this license.
- Red junglefowl from Wikimedia Commons, user Charles J. Sharp , under this license. Modification: I cropped the photo.
- Images of Zani on the snuffle mat and Clara playing with the flirt pole copyright Eileen Anderson.
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11/04/2025