I saw in the newspaper yesterday an advert for an 'ultrasonic and electromagnetic' mouse and rat repeller. That got me interested. The ultrasonic bit seems to be plausible enough - I don't know much about rodent ear physiology, but I'm willing to believe they can hear sounds at higher frequency to us and to dogs and cats (which, the advert claims, are unaffected.) It's the electromagnetic bit that has me interested.
A bit of googling has got me some sciency-sounding but not very useful explanations - e.g. "The electromagnetic function uses every electrical cable in the building to carry and transmit a signal, which can be detected by the pests up to 1 metre from any cable, even inside wall and ceiling spaces" - from http://www.gardencentreonline.co.uk/Garden-Accessories-Pest-Control-Ultrasonic-Electromagnetic-Pest-Repeller-2000/1452-PD/default.html
Cables to carry electromagnetic signals? That's perfectly reasonable - an electrical signal on your house supply is how your electricity company can switch power on and off to your hot water cylinder remotely, for one thing. But what sort of signal, and what does it do to our rodent friends, and, moreover, why doesn't it do the same to us?
"This Repeller also sends pulses through the existing wiring within the house or property and by changing the electromagnetic field, helps to create an environment within the walls, floors, and ceilings which pests would rather leave. " From http://www.pestrol.co.nz/shop/Pestrol+2+in+1+Rat++Mice+Repeller/Pestrol+2+in+1+Repeller.html
That's slightly more informative, but still has a pseudo-science ring to it. A bit more googling and I discover this phenomenon isn't just used to drive out rodents.
"This aggravates the nervous system of the spiders and drives them out from their hiding places and banishes them for good". From http://cgi.ebay.co.uk/SPIDER-REPELLER-ELECTROMAGNETIC-REALLY-WORKS-/250720293044?pt=LH_DefaultDomain_3
So we are on 'aggravating the nervous system now'. A quick search on ISI Web of Science for journal articles on spider, nervous system and electromagnetic waves is giving me nothing. But what I do know is that there have been lots of studies on things like cell phones and people, which show that there isn't much effect of EM waves on people (unless you get up to X-rays and gamma-rays), so I'm wondering why it would be different for other animals.
Anyway, to summarize, I'm intrigued. Does any one have ideas as to what these machines are 1. actually doing with your household wiring, and 2. what is the effect on the mouse / rat, and 3. why don't we and cats / dogs respond in the same manner? (Remember, it's the electromagnetic bit I'm puzzled by, not the ultrasonic.)