John et al
It looks like the use of cameras & PIRs would be too easy to defeat. Perhaps we do need to look towards a burglar alarm installation with concealed reed switches although I've yet to see the property.
Barry
Barry Taylor, Clinical Scientist
Medical Physics Department
Tulley Medical Physics Building, Hull Royal Infirmary
Anlaby Road, Hull HU3 2JZ
Tel 01482 675928, fax 01482 675750
-----Original Message-----
From: A discussion list for Assistive Technology professionals.
[mailto:[log in to unmask]]On Behalf Of John Hennock
Sent: 03 June 2005 14:35
To: [log in to unmask]
Subject: Re: movement detectors
Barry
Interesting problem which raises a number of issues.
Are you suggesting that this youth would deliberately sabotage a PIR or
other device to ensure that it would not raise an alert? If so, you have an
interesting specification problem.
Ideally, you would wish to protect / detect within the immediate area of the
window. This means that you do not have to filter out normal and acceptable
movement or activities within the room. If you wished to use PIR detectors
to identify movement within the window recess, then there are some very
compact designs which detect along a narrow strip. These are known as
curtain detectors. However, you will need to wire these devices as they are
not large enough to contain a radio module and batteries. Remember that any
PIR device will not be effective if there are items which can obstruct the
line of sight, e.g. blinds or curtains.
If the youth is intent on damaging or disabling these detectors, then you
need to consider how to detect such an attempt. There are two risks:
destructive impact or masking.
In terms of impact, given their compact design, they do not present much of
a surface for impact, although they are not necessarily designed to be
"vandal resistant". If he did smash the detector, there is a possibility
that he would cause sufficient damage to break the circuit and trigger an
anti-tamper alert.
The issue of masking is more subtle. The detectors could be masked by
hanging materials within their line of sight, or by covering the detector
lens with a material such as paper tape. It is possible that such an act
would trigger the alarm but, as the boy would still be in his room, this
might be mis-understood to be a false alarm and ignored. Once masked, the
detectors would no longer be able to detect movement.
The issue of masking PIR detection is one that has exercised Cenelec for a
few years now and, given the nature of the discussion, you should not expect
an early technical solution. The safest affordable mechanism to deal with
masking would be to install at least two detectors in a manner that ensured
that each covered the area in which the other was installed. (Masking both
would generate two false alarms.) You might also consider fitting curtain
PIR detectors above the window on the outside wall, providing that you can
find a suitable waterproof device. The risk with this installation is that
it could be triggered by a cat on the window cill.
Use of window sensors would provide you with a reliable indication of
whether the window had been opened. However, if the window is normally part
open at night for ventilation, you would be none the wiser.
Given that you will have to use wired detectors, then I would recommend
using an intruder alarm control panel. This means that you can protect /
detect damage to the wiring via the anti-tamper detection circuit that is
standard within such equipment. It is possible that the family might regard
an intruder alarm as being of general benefit and would be happy to pay for
the installation. Given the application, I would suggest that you use a
multi-zone system and that the bedroom in question be assigned to a unique
zone.
I trust this helps.
Regards,
John Hennock
Director, HPS Consulting Ltd - Management and telecare consultants
Tel +44 (0)121 314 8066 (DD +44 (0)1427 677545)
Fax +44 (0)870 762 7696
Web: www.hpsconsulting.com
-----Original Message-----
From: A discussion list for Assistive Technology professionals.
[mailto:[log in to unmask]] On Behalf Of Taylor, Barry
Sent: 03 June 2005 12:45
To: [log in to unmask]
Subject: movement detectors
Dear all (& particularly Guy - I've lost you address)
I've had a teenager referred who frequently escapes from his bedroom at
night, leaves the house and causes damage. We are looking for a vandal
proof PIR and/or door/window sensors to alert his parents in another room.
I'm aware that some reed switches can be buried in the woodwork, but I
wonder if a rugged (& almost invisible) PIR might be an easier solution.
Barry
Barry Taylor, Clinical Scientist
Medical Physics Department
Tulley Medical Physics Building, Hull Royal Infirmary
Anlaby Road, Hull HU3 2JZ
Tel 01482 675928, fax 01482 675750
--
This email has been verified as Virus free
Virus Protection and more available at http://www.plus.net
|
