How do ultrasonic devices built to scare away animals such as cats work? Do they mimic a high-pitched sound known to scare such animals, or do they scare them simply by their loudness? Perhaps it is just that the sound annoys the animals as much as it annoys me.
鈥� These devices offer a modest deterrent effect 鈥� at best. A cat鈥檚 personality and whatever it sees as its incentive for straying into a garden are likely to trump most attempts to keep it away.
A trial in suburban gardens suggests that these gadgets can cut the frequency of cat intrusions by about a fifth, and that those that do occur last a third less time. The combined effect is that cat traffic is halved.
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Another trial, this time in the lab, introduced cats to the test area well beyond the device鈥檚 stated range, with food arranged at 1-metre intervals from the device. Cats within earshot of it were less inclined to forage actively, but lingered longer than those at a distance. The only apparent sign of discomfort was an increase in ear-twitching.
Similar high-frequency devices built to deter loitering teenagers work on the premise that adults will be less affected, as they may have lost the ability to hear high-pitched sounds. Other products play classical music or whatever genre the makers deem unlikely to appeal to the average teenager.
There is an urban myth that what has become known as the 鈥渂rown note鈥� can be used to disperse crowds. The idea is that people lose control of their bowels when exposed to sound at a frequency of around 5 to 10 Hertz, too low to hear but supposedly able to resonate in the body.
鈥淚t鈥檚 an urban myth that the 鈥榖rown note鈥� 鈥� sound at 5 to 10 Hertz 鈥� can make you lose control of your bowels鈥�
This myth seems to stem from research carried out as part of the US space programme. There were concerns about the stresses astronauts would experience at launch, so their physiological responses were tracked while they were strapped into their cockpit seats and subjected to mechanical vibration. The astronauts experienced serious bowel and other bodily discomfort because the vibration could reach their bodies via the seats. Air, in contrast, is poor at transferring low-frequency vibration as sound.
In cowboy films, characters may put an ear to railway tracks to 鈥渓isten鈥� for an approaching train, supposedly audible through vibrations travelling through the rails. In fact Hollywood is guilty of poetic licence because the vibrations can only be felt, not heard.
Needless to say, don鈥檛 ever try this yourself, whether the railway is electrified or not.
Mike Follows, Sutton Coldfield, West Midlands, UK
This article appeared in print under the headline 鈥淪caredy cats鈥�