Re: home made home security

[Frank Olson <use_the_email_links@xxxxxxxxxxxxxxxxxxxxxx>]

Doug Meredith wrote:
> "Robert L Bass" <Sales@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
>> "Frank Olson" <use_the_email_links@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
>> news:DBIBk.34830$QF5.14826@xxxxxxxxxxxxxxx
>>> mentari wrote:
>>>
>>>> The problem with PIR is that all a crook does is don a heat insulating
>>>> suite and simply walks pass the sensor - it won't pickup the heat.
>>>
>>> A-A-hahahahahahahahahahahahahaha!  Priceless!
>> Just so you'll understand, the reason Frank laughed is that idea is a fable.
>
> I'm a little late to this thread but I don't believe this is a fable.
> I was experimenting with this earlier in the week and I can walk right
> past my motion detectors by wearing a winter jacket and hiding my face
> or by holding a blanket up.
>
> Doug


Yeah?  What's the make and model of the detector?  How is it mounted?
Without getting into ways of defeating motions, you have to understand
how they work.  PIR's utilize a faceted lens.  In order to sense
"motion" you have to walk across the face of the lens (perpendicular to
the detection zones).  Old style ultrasonic and any microwave type
motion sensor depends on the doppler shift of a target moving TOWARDS
the detector.  A PIR has a difficult time picking up motion when you
move towards it.  A microwave detector would have a hard time picking
you up if you walked across it's field of view whilst maintaining your
distance from it.  There are "combo" units made up of a microwave
element and a PIR.  In most instances both detection methods have to be
tripped for a valid motion "event".  If you walk slowly enough, you
could fool most of the cheaper detectors (and even some of the more
expensive "pet proof" ones).  I run into customers that have to "test"
the "quality" of the sensor by using the "shuffle across the floor with
your head down and back bent" method all the time.  I can assure you
that the average thief isn't going to be doing an "old man" impression
when he breaks into your house to try and fool your motion sensors.
Besides, in a properly set up perimeter type security system the motion
sensors are there as a "backup" (or to protect a special area) and
you'll get an alarm generated *BEFORE* he even sets foot in the house.