"PJO" wrote in message ...
NT wrote:
I'm not having a pop at you NT. I'm just using your post as an example of
how wrong terminology and poor advice can cause more confusion that it's
worth. We're talking security here and it's not good to give outdated advice
and non-suitable idea's.
No worries
If I'm wrong keep saying, and together we all learn.
Second be careful where you mount door opening detectors, as door
warping or wind can set them off. They are a big source of false
alarms.
Is it? I've never heard of it. The average magnetic contact has an operating
gap in execss of 20mm. Newer ones will stretch to 80mm! That's some warped
door!!! As for wind... I have never known wind to cause a door contact to
operate. That is unless the door is blown open!
That sounds different to the ones I've had experience with. They didnt
have anything like 20mm to play with, and proved to be useless. They
were affected by warp, wind, you name it. The ones that were
decommissioned were magnets and reed relays. But if things have moved
on, good, I gather they have.
Third cover your desired area with more than one technology. Only when
both detect an intruder do you want the system to go off. Most sensors
are prone to some cause of false alarm or other.
Usine two detectors in parrallel is another idea but is messy. Dual-tec
detectors do the job well.
Yes, this is another way of implementing the above, rather than
implementing it at the control panel. Either way, 2 detection events
by 2 different technologies are needed to avoid false alarms.
Glass break sensors are useful (not foil strips).
With respect... glass breaks detectors are useless because the ultra-sonic
sound they rely one (breaking glass) can be caused be many other natural
sources. Fridge motors is a good example! I remember in the early 80's when
these bacame popular. We installed hundreds of them in schools, shops and
the like. Then the kids discovered that if they through milk bottles outside
the window the bloody alarm would activate! No, forget break glass
detectors.
Youre describing early ones, which were problematic as you say. Things
have moved on. All detectors have false trigger modes, these included.
What you describe is the result of using low tech detectors and using
a control panel that (wrongly) triggers from just one detection event.
If you use them with another detector type, with 2 events being
required for system trigger, you have a sound system. Or just use a
modern glass break detector with proper discrimination.
Here we go:
http://web.raex.com/~colombo/security/secmis9.htm
"Older models were plagued by false alarms. This is because they did
very little filtering and even much less audio processing to tell the
difference between a valid sound and one that is normal to the
environment. More recent designs now use microprocessors to digitize
and process the audio sounds picked up in an environment. This enables
them to discern the difference between the sound of a window breaking
and that of a broken drinking glass."
This explains why modern ones are reliable and effective, and
incorporate the tech you mentioned above:
http://web.raex.com/~colombo/security/secmis10.htm
As for window foil. It's outdated by many other forms of setection such as
curtain PIR's etc. You can't even buy the proper foil and blocks these days.
It is around, just not popular. Google. Also, copper adhesive foil
used in lead window making can be used effectively.
Handbook of Loss Prevention and Crime Prevention,
Butterworth-Heinemann:
"In the past, foil tape was the most common way that security
installers electronically secured window glass. Although it is not as
common today, foil tape is still used by alarm installers who are
skilled enough to work with it. In fact, many of them swear that it
works better than any of the electronic devices--called glass-break
detectors--used by other installers.
"Metallic foil...is widely used to detect glass breakage in show
windows, doors, and transoms. When the glass cracks and breaks the
foil, it interrupts the low voltage electrical circuit and activates
the alarm"
http://web.raex.com/~colombo/security/secmis10.htm
"The presence of foil tape on windows is an automatic sign that a
burglar alarm system is employed on the premises. Most burglars would
rather not break into a facility that has one."
Smoke bombs eh?! Corr!
Yup, they work by disorientating the burglar, and making them realise
they are out of control of the situation. If you have a large valuable
premises, using these by entrances halls stops many burglaries in
their tracks.
The disorientation makes it take a long time to simply get back out of
the building, thus improving odds of arrest, as well as being visible
to passers by.
I did say if you had money to spend: this is not really your usual 2
up 2 down kit
Burglar identifying paints?? Don't think so. You've been watching too much
007!
http://www.screwfix.com/app/sfd/cat/...52567&id=16822
cost £7:49.
There are also more technological ones available, which stain the skin
indelibly, but the simple cheap option above is suited to diy use on
drain pipes etc. They both deter and help catch afterwards.
Finally tamperproof wiring is a bonus to protect against the more
determined attackers, but you dont need this in most cases.
A/T wiring has been standard since the 60's and is an absolute must.
a must? why?
It's
not just there to warn of attack but also to give alert to damaged wiring
etc.
etc?
Of course it all costs money, hence the temptation to go for a
cheapass solution. Trouble is, 3 PIRs and a single event tripping
system isnt really a solution.
But it is if it does the job. In my time I have installed thousands of 3 PIR
systems with panels that have no more than a single knoxk circuit. They
rarely false alarms and always activated on intrusion.
My own experience with PIRs makes that hard to imagine. Perhaps either
youre using PIRs that require 2 events to trigger, or use dual
technology, or else PIRs have suddenly come a long way?
Over to you.
Regards, NT