[Noisebridge-discuss] The rats are getting ballsy

[Tomm]

I ordered a package of 4 of the Pestchaser ultrasound rodent repellers
Rubin mentioned.  My day job is in ultrasound, and I want to take one of
the apart and see what they're doing.  They're almost certainly using
PZT piezo crystals to achieve the stated 5-7 year battery life, but I
want to see what drive circuitry they're using.  I'll install the other
3 at noisebridge - probably won't hurt. 

No one will be able to hear these devices at a distance of >50cm or so. 
The Pestchaser uses 32khz to 62khz ultrasound, which is far outside
human hearing range.  Most people can hear up to about 20khz, some up to
about 23khz (myself included), but no one has ears that can directly
hear a 32khz sound.  

The 40khz air ultrasound devices I work with are barely audible at about
10cm, but mostly because it's so damn loud (115dB) that the 20khz,
10khz, and 5khz harmonics created in the ear are loud enough to be
perceived. It's a pulsed device, and sounds like a "tic" when running,
not like high-frequency tone.  So, while one might hear a little bit of
tic'ing if you put the Pestchaser next to your ear, there's no way
you'll near it if it's near the floor and you aren't lying down next to
it.  For comparison, a plane taking off from 10m away is 115dB.

Even dogs can barely hear 40khz.  See this graph:
http://www.lsu.edu/deafness/HearingRange.html  , where their perception
of loudness drop about 60dB between a 30khz signal and a 40khz signal. 
Humans have a comparable drop between 15khz and 20khz.  40khz is right
out.  Mice, on the other hand, hear just fine at 40khz, with the
distress call of a young mouse at about 40khz (after all, mice don't
want their distress calls to attract the cat, let alone a human!).

I've been dubious of the ultrasound devices for pest control.  As anyone
in the Cyborg group will tell you, any consistent stimulus will
eventually be integrated into your brain, and rodents would just because
used to the sound.  The Pestchaser manufacturer claims that it puts out
a non-periodic sound and that rodents can't become habituated to it,
which I'm skeptical of but I suppose it might work just by annoying
them.  After all, rats live in subway tunnels right next to trains
rushing by at 130dB+.  The pestchaser says that it sends out a special
46.5khz sound that mimics the sound of a dominant mouse, which sound
nifty but likely doesn't help with rats.

Speaking of which, I'm pretty sure that ultrasound repellers will work
far better with mice than with rats. Mice are at the bottom of the food
chain, and anything that moves likely wants to eat them.  A lab
researcher friend (that is, um, very much not a vegan) says that it's
impossible to get mice to relax  Rats, on the other hand, are smart
badasses that chill out all the time, as any rat pet owner will tell
you.  Pestchaser claims to have been effective with rats, but I'd guess
their "15 of 17 sites cleared" claim were mostly mice sites, with
perhaps a few rats deciding that there are easier targets without all
this racket.

That all said, my experience backs up what I've been told by pest
control professionals: plugging holes works the best.  Rats can fit
through an opening the size of a quarter, and mice the size of a dime. 
Plug them up, and they're less likely to enter not only because of
chance (hey look, an open hole!) but because there are a lack of exits
(oh shit, nowhere to escape to!)  Spackle won't work because they'll
just eat through it.  High density urethane spray foam, available at
most any hardware store, is your friend.  I inherited a minor rat
infestation at a house in Berkeley, and two cans of spray foam later, I
never saw rat traces again.

    Tom

On 2/24/2010 1:08 PM, Rubin Abdi wrote:
> ====Ultrasonic====
> * Get ultrasonic emitters. 
> [http://www.amazon.com/Victor%C2%AE-PestChaser%C2%AE-Ultrasonic-Rodent-Repellent/dp/B0015WM4QA/ref=sr_1_4?ie=UTF8&s=home-garden&qid=1267045186&sr=8-4]
> * Set them up outside of the space.
> ** At the end of the ledge holding the lights in the main stairs.
> ** In the not-a-fire-escape stairwell.
> ** At the bottom of the stairs under the DJ booth.
> * See if any humans can hear them.
>
> ====Peppermint====
> * Get some peppermint.
> * Spread it around the space without stinking up the space.
>
>