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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.consumers
Subject: Re: Infra-red /microwave detectors; for use as exterior people detectors
Message-ID: <710@kitty.UUCP>
Date: Wed, 15-Jan-86 09:22:34 EST
Article-I.D.: kitty.710
Posted: Wed Jan 15 09:22:34 1986
Date-Received: Fri, 17-Jan-86 00:42:30 EST
References: <211@hropus.UUCP>
Distribution: na
Organization: Recognition Research Corp., Clarence, NY
Lines: 55

> I was wondering is anyone had the inside track on infrared detectors
> or microwave detectors (e.g., those little units at supermarkets that
> open doors).  I would like to hook one up on the outside of my house.
> I figure this would greatly discourage vandalism and petty theft ...

	Most of the door opening detectors are microwave since changing
outdoor illumination (i.e., movement of the clouds, precipitation effects,
etc.) can cause false operation of infrared detectors.  Infrared detectors
are fine - INdoors.

> 3).  Another alternative might be these sound switches that activate
> lights.

	Forget it - you will have a false trigger problem with vehicles,
aircraft, birds, etc.

> I'm not sure how water-resistant they are.  With an infrared detector,
> I could presumably put it inside a plastic box (I hope infrared passes
> thru clear plastic - anyone know for sure??????????????)

	Most plastic (and glass) severely attenuates infrared energy so
that a passive infrared intrusion detector will not function if the sensing
element is behind such a window.  If you look closely at a passive infrared
detector, you will see that the covering of the detector surface is very thin,
special plastic - the sensing element is directly behind this cover.

> The infrared units seem to be ideal, supposedly triggered by
> specific body temperature of a person (although I wonder about
> the effects of a hot summer or freezing winter night; I mean, your
> normal skin temp is about 85 - will the detector see anything if it's
> 90 degrees out???  Or if it's 10 degrees with the wind blowing, will
> you still give off sufficient heat?

	That's why infrared detectors are not used outdoors.  Also, a person
dressed in well-insulated clothing will often not be detected by a passive
infrared detector indoors, let alone outdoors.  The infrared detectors work by
sensing a CHANGE in infrared energy over a short period of time, with such a
change being interpreted as motion.  Preciptation and other outdoor effects
can often cause such detectable change in short periods of time, thereby
resulting in false triggering.

	Unquestionably, you want a microwave motion detector, which is pretty
much immune to all but the most severe outdoor precipitation effects.  I
would suggest that you forget about Heathkit and Radio Shack and try to
find a commercial distributor of alarm products to visit; many larger
locksmiths also distribute alarm components.  One manufacturer of microwave
detectors which would be suitable for yoru purpose, and which is commonly
stocked is Racal.

==>  Larry Lippman @ Recognition Research Corp., Clarence, New York        <==
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