Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hplsla!tomb
From: tomb@hplsla.HP.COM (Tom Bruhns)
Newsgroups: sci.electronics
Subject: Re: How can I fool the motion sensors connected to our lights?
Message-ID: <5170044@hplsla.HP.COM>
Date: 19 Jul 89 16:09:31 GMT
References: <358@gorn.santa-cruz.ca.us>
Organization: HP Lake Stevens, WA
Lines: 32

larry@kitty.UUCP (Larry Lippman) writes:
>	Passive infrared detectors (PIR) for use in security and energy
>management systems detect MUCH longer wavelength IR, with typical spectral
>sensitivity in the range of 2 to 12 microns (2,000 to 12,000 nm).  The
>actual characteristics of these sensors depend upon the sensor manufacturer
>and the bandpass of the protective cover.  The cover will, for example,
>typically NOT pass any energy below 2 microns so as to preclude interference
>from ambient light.  After all, the function of a PIR is to detect body heat,
>and NOT be influenced by the effects of ambient light.  NIR is too close
>to ambient light to be detected.
>
><>  Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
><>  UUCP   {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry
><>  TEL  716/688-1231 | 716/773-1700  {hplabs|utzoo|uunet}!/      \uniquex!larry
><>  FAX  716/741-9635 | 716/773-2488     "Have you hugged your cat today?" 
>----------

The PIR detectors used in my house to turn on/off lights are sensitive to
the heat of a woodstove and to direct sunlight (perhaps interrupted by
swaying trees).  This may give you some ideas:  for example, you could
pulse a 300W/120V lamp with, say, 10 or 20 volts, and get a lot of IR
but not much visible light.  If you know where the sensor is, you could
focus the IR toward it.  Also interesting to note:  In the (real) old
days of IR spectrometry, spectrometer rooms were lined with 100 watt
lights; if you moved from one place to another, you were supposed to
turn on a light where you left and turn one off where you went.  That
was supposed to cause the least disruption to the IR background.  So
you are probably roughly equivalent to a 100 watt lamp in an IR sense.

(Experiments may show you can get by with something much smaller than
the 300W lamp suggested; you could try a "heat lamp" with integral
reflector envelope for focussing...)