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Mark Mann Few of us would put up with a TV that emits an annoying whine or a light bulb that flickers, but for our pets, that may the world around them.

Their senses are tuned differently than our own and may detect a cacophony of noise and strobe effects that we don't, particularly as we fill our homes with technology. You can fix a beeping smoke detector quickly by changing the battery, but it might also be emitting a constant high-pitched noise that only your dog can perceive. Have we built them an unintended hell?

Dr. Sheila Carrera-Justiz, assistant professor of neurology at the University of Florida College of Veterinary Medicine, says that our pets' sense of hearing makes the world a far different place for them than for you and me. They hear everything we do, plus much more. "I recently got a new dishwasher and it's really quiet -- my dogs don't react to it at all," she says. "But [the sound of] the garbage truck going by? That's a different story."

Ultrasound: The unheard screech
Dr. Katherine Houpt, an environmental factors expert at Cornell University's College of Veterinary Medicine, says pets routinely respond to sound above the frequencies humans can hear, called ultrasound. "Many dogs are afraid of smoke alarms," she says. "So the dog is going crazy and the owner doesn't know why."

Humans nominally hear sound that ranges in frequency from the lowest bass around 20Hz, or cycles per second, up to the highest, tingling treble near 20,000Hz. In reality, adults may only hear half of that range, as age reduces our sensitivity to high pitches.

But dogs can hear sounds up to 45,000Hz and cats up to 64,000Hz. To them what we call "ultrasound" is just sound, but our gadgets aren't designed with that in mind. Meant to appeal to human buyers, consumer electronics eliminate only the high-pitched noise that we hear. Our household pets can be left with an unconsidered residual. 

The very concept of "ultrasound" is a human-centric prejudice: For dogs and cats, the higher frequencies we consider to be ultrasound are just part of their normal continuum of hearing.

CNET Silencing those sounds
What happens next isn't so clear. While we know that animals hear a vast amount of sound we're deaf to, we don't have as clear a handle on how it may affect them. One possibility comes from Dr. Jeremy G. Turner of the Southern Illinois University School of Medicine Department of Pharmacology. In a 2005 study on the effects of noise on lab animals, he noted that noise can alter the heart, sleep and endocrine cycles in animals and make them more susceptible to seizure.

A 2015 survey by a consortium of veterinary groups in the UK linked seizures in some cats with a phenomenon called feline audiogenic reflex seizures caused typically by high-frequency sounds. The study named over a dozen ordinary household noises that appear to be a cause, including phones ringing, computer printers and even the crinkling of aluminum foil.

Completely ending those sounds in your home would be very difficult, and it's hard to judge the severity of the problem because there's no rating or labeling of ultrasonic emissions on consumer electronics -- and our pets can't tell us what's bugging them. Still, there are things you can do. 

This animated screen grab shows the difference in overall sound when the components in a typical media room are turned off and then on. The largely blank screen shows the off state, the screen with more green bands shows the sounds you can hear (lower green peaks and valleys) and those only your pets can hear (upper blue and green bands).

CNET Strategies to reduce these sounds include turning off components at the plug when not using them (which has the added benefit of stopping expensive phantom power draw), though this may interrupt the function of something like a DVR. You can also set up at least one room in your home as a quiet room, free of most or all electronics including LED lights. 

Steps to reduce electronic pollution at home 

Switch off devices at the plug when practical (and save on phantom power draw). 

Create a quiet room in the home with no electronics or LED lights. 

Locate home media equipment in a closet or garage to isolate ultrasound (as well as whine and fan noises you can hear as a bonus). 

Shop for LED lights with low flicker ratings on LEDBenchmark.com (though it has recently stopped adding new reviews).

If you have a dedicated home theater, you can reduce noise for both you and your pet by remote mounting equipment like receivers, amplifiers, DVD players and DVRs (fan noise can be especially irritating). That will involve some longer cable runs and is typically considered a high-end home theater option, but may not be that difficult by using a converted linen closet next to the media room with a couple of in-wall cables to the TV and sound bar. 

But some of the worst offenders may be the ones that are hardest to control. We recorded the sound signature of each component in our sample media room by itself: Two of the clearest ultrasound signatures came from the LED bulb in a table lamp and the 42-inch LCD TV on the wall.

Turning on one component at a time shows that a PAR 30 LED lamp bulb added significantly the a room's ultrasonic sigatures, but turning on the 42-inch LCD TV -- even with nothing playing on it -- added the most.

CNET Flicker: The disco that never stops
It's not just unheard noise your pet may be dealing with but also unseen light flicker. LED lighting is taking over the home, with 40 percent of the $26 billion US LED lighting market going to residences as of 2016, according to Zion Market Research. But LED lights have the inherent problem of flickering on and off all the time, whether dimmed or at full brightness. You may barely detect flicker from a modern LED bulb, but as with sound, your pets have a greater range of perception. Add a disco ball to that high-pitched whine.

David Wren, managing director of PassMark Software in Sydney, blames LED bulb flicker on cheap parts. LED bulbs are DC devices that run on household AC wall power which must be converted before it feeds the LEDs in the bulb. In most bulbs, the electronics that perform that conversion do a crude job, with flicker as a by-product.

In humans the critical flicker fusion (CFF) threshold, or the frequency at which a light appears to be completely steady to the observer, can be as low as 24Hz or 24 "flickers" per second. Most online video is based on 30 frames per second, including everything you watch on CNET. To the human eye, that degree of "flicker" appears to be fluid, smooth motion.

But as Alexandra Horowitz writes in her book Inside of a Dog: What Dogs See, Smell and Know, canines have a more sensitive CFF of up to 80Hz or 80 flickers per second. "This might explain why most dogs cannot be planted in front of the television to engage them," she writes. "It doesn't look real."   

Seen visually, the ultrasound emitted by common home tech becomes as stark to the eye as it may be to your pet's ears. 

CNET Going flicker-free
Here, as with ultrasound, the exact effects of light flicker on pets are unknown, but research has provided some clues. Dr. Richard Inger at the University of Exeter says that "flickering light can have detrimental effects on a number of other animals, so it's certainly possible that flickering light might have detrimental effect on cats and dogs." And a 2006 study by Southwick's Zoo in Mendon, Massachusetts, and Sacramento City College in California found that a flickering light may cause fear in animals.

Many LED lights' flicker ratings can be found on rating site LEDBenchmark.com. Consider buying lights with lower numbers in both flicker percent and flicker index.

Unless you're planning to move off the grid, you aren't going to banish the sound and light polluting technologies from your home. But with so many people just starting to adopt smart home tech in particular, there are fresh opportunities to err on the side of our pets in an area that isn't fully understood. You can have the home theater of your dreams, energy-saving LED lighting and a smoke detector that you can monitor from your phone, but consider your pets in the process. Remember, they live there, too.  

This story appears in the Spring 2018 edition of CNET Magazine. For other magazine stories, click here.

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