As Christmas approaches we wanted to display the cards that we've
received so we hung some colourful ribbons vertically on a wall and
attached the cards to them.

The next morning we set the alarm as usual, locked up the house and
went shopping. Shortly afterwards we received a message saying that our
alarm was sounding. We went straight back home and to our great relief
found that the house was quite secure, and then called the alarm company
to report the false alarm.

Their technician came along quite quickly, confirmed that our alarm
system was working properly and then pointed out that our ribbon-mounted
cards were hanging over a radiator. The heat rising from that radiator
was causing some of the larger cards to flap in the 'breeze', and this
was being detected as movement by the room sensor which then activated
the alarm as it was supposed to do. Entirely obvious with hindsight.

The alarm technician said that at this time of year they usually
receive quite a few call-outs to false alarms caused by the heat rising
from radiators and causing decorations to move.

We've now repositioned the ribbons with cards to another wall which has
no radiator underneath.

Others in this NG might care to take note. Happy Christmas.

--
David C.Chapman - )
--------------------------------------------------------------------------

On Thu, 13 Dec 2012 14:42:04 +0000, David Chapman
wrote:


As Christmas approaches we wanted to display the cards that we've
received so we hung some colourful ribbons vertically on a wall and
attached the cards to them.

The next morning we set the alarm as usual, locked up the house and
went shopping. Shortly afterwards we received a message saying that our
alarm was sounding. We went straight back home and to our great relief
found that the house was quite secure, and then called the alarm company
to report the false alarm.

Their technician came along quite quickly, confirmed that our alarm
system was working properly and then pointed out that our ribbon-mounted
cards were hanging over a radiator. The heat rising from that radiator
was causing some of the larger cards to flap in the 'breeze', and this
was being detected as movement by the room sensor which then activated
the alarm as it was supposed to do. Entirely obvious with hindsight.

The alarm technician said that at this time of year they usually
receive quite a few call-outs to false alarms caused by the heat rising
from radiators and causing decorations to move.

We've now repositioned the ribbons with cards to another wall which has
no radiator underneath.

Others in this NG might care to take note. Happy Christmas.

Sometimes the warm air convection alone is all that's required.

--
Graham.
%Profound_observation%

In article ,
David Chapman writes:

As Christmas approaches we wanted to display the cards that we've
received so we hung some colourful ribbons vertically on a wall and
attached the cards to them.

The next morning we set the alarm as usual, locked up the house and
went shopping. Shortly afterwards we received a message saying that our
alarm was sounding. We went straight back home and to our great relief
found that the house was quite secure, and then called the alarm company
to report the false alarm.

Their technician came along quite quickly, confirmed that our alarm
system was working properly and then pointed out that our ribbon-mounted
cards were hanging over a radiator. The heat rising from that radiator
was causing some of the larger cards to flap in the 'breeze', and this
was being detected as movement by the room sensor which then activated
the alarm as it was supposed to do. Entirely obvious with hindsight.

The alarm technician said that at this time of year they usually
receive quite a few call-outs to false alarms caused by the heat rising
from radiators and causing decorations to move.

We've now repositioned the ribbons with cards to another wall which has
no radiator underneath.

Others in this NG might care to take note. Happy Christmas.

Christmas decorations, balloons bobbing around, garlands rotating
in a micro breeze, etc are common causes at this time of year.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article , Andrew Gabriel
writes

Christmas decorations, balloons bobbing around, garlands rotating
in a micro breeze, etc are common causes at this time of year.

You can get PIRs which are configurable to trip after one, two, or three
activations, usually by link selection. Sounds like one of those might
be useful for the OP.

--
(\_/)
(='.'=)
(")_(")

On 13/12/2012 16:28, Mike Tomlinson wrote:
In article , Andrew Gabriel
writes

Christmas decorations, balloons bobbing around, garlands rotating
in a micro breeze, etc are common causes at this time of year.

You can get PIRs which are configurable to trip after one, two, or three
activations, usually by link selection. Sounds like one of those might
be useful for the OP.



This is alarm system parlance is referred to as "double knock"

its the panel itself that has to support "double knock" rather than the
PIR, also I am prepared to be corrected on this point.

I've seen it used mostly on magnetic door switch sensors and sometimes
on smoke detectors located near kitchens or bathrooms

On 15/12/2012 11:34, Stephen H wrote:
On 13/12/2012 16:28, Mike Tomlinson wrote:
In article , Andrew Gabriel
writes

Christmas decorations, balloons bobbing around, garlands rotating
in a micro breeze, etc are common causes at this time of year.

You can get PIRs which are configurable to trip after one, two, or three
activations, usually by link selection. Sounds like one of those might
be useful for the OP.



This is alarm system parlance is referred to as "double knock"

its the panel itself that has to support "double knock" rather than the
PIR, also I am prepared to be corrected on this point.

I've seen it used mostly on magnetic door switch sensors and sometimes
on smoke detectors located near kitchens or bathrooms

That would be because you use pulse counting circuits in PIR sensors.
If they count three or four pulses then you usually want the alarm to
trigger.

In article ,
Stephen H writes:
On 13/12/2012 16:28, Mike Tomlinson wrote:
In article , Andrew Gabriel
writes

Christmas decorations, balloons bobbing around, garlands rotating
in a micro breeze, etc are common causes at this time of year.

You can get PIRs which are configurable to trip after one, two, or three
activations, usually by link selection. Sounds like one of those might
be useful for the OP.



This is alarm system parlance is referred to as "double knock"

its the panel itself that has to support "double knock" rather than the
PIR, also I am prepared to be corrected on this point.

Two different things...

PIRs can be configured for how many detections/pulses before
they trigger. This depends what you're using it for. For a light
switch or triggering a CCTV recording, you would select just
one, so it happens instantly you come into to view, and false
triggers don't matter. For an alarm output, you would select
two or three, to reduce false triggering from something like
a moth, but if used to switch on a light, it probably wouldn't
switch on until you got well into the detection area, or in
a recording, you would miss the entry. (This does present a
challenge when you use a PIR for both alarm and home automation.)

"double knock" in a panel is the ability for a panel to go
into higher security mode on a first trigger (which might
generate a monitoring station warning), and full alarm
if there's another trigger in something like 5 minutes.
"double knock" works across multiple sensors, so one PIR
triggering once, and another one triggering once will
generate a full alarm.

For a police response on new systems now, I believe the rules
are that two different sensors must be triggered, whereas
"double knock" from a single PIR sensor used to be acceptable.

I've seen it used mostly on magnetic door switch sensors and sometimes
on smoke detectors located near kitchens or bathrooms

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

En el artículo , Stephen H
escribió:

its the panel itself that has to support "double knock" rather than the
PIR, also I am prepared to be corrected on this point.

I can believe that some panels support double-knock, but the PIRs I've
seen are designed to only open the loop after n triggers, where n can be
selected by links. They're interchangeable with standard PIRs and don't
need anything special in the panel.

Some of them have LEDs like a mini bar graph. They have three LEDs, if
one or two light up the alarm isn't triggered but getting three does.

--
(\_/)
(='.'=)
(")_(")

In article , Mike Tomlinson
writes
En el artículo , Stephen H
escribió:

its the panel itself that has to support "double knock" rather than the
PIR, also I am prepared to be corrected on this point.

I can believe that some panels support double-knock, but the PIRs I've
seen are designed to only open the loop after n triggers, where n can be
selected by links. They're interchangeable with standard PIRs and don't
need anything special in the panel.

It's handy if you have shock sensors in the system, I have set up
external sounders to go off for the duration of a shock event but only
trigger the alarm for repeat events. Ideal for an apartment setup with a
tough outer door, the monkey gives up in short order if a kick to the
door results in a short deafening burst on a nearby sounder without the
need for a full 20min activation.
--
fred
it's a ba-na-na . . . .

Yes been there many years ago, it was far worse with ultrasonic sensors but
I guess the principal is the same.

Brian

--
From the Sofa of Brian Gaff Reply address is active
"David Chapman" wrote in message
...

As Christmas approaches we wanted to display the cards that we've
received so we hung some colourful ribbons vertically on a wall and
attached the cards to them.

The next morning we set the alarm as usual, locked up the house and went
shopping. Shortly afterwards we received a message saying that our alarm
was sounding. We went straight back home and to our great relief found
that the house was quite secure, and then called the alarm company to
report the false alarm.

Their technician came along quite quickly, confirmed that our alarm
system was working properly and then pointed out that our ribbon-mounted
cards were hanging over a radiator. The heat rising from that radiator was
causing some of the larger cards to flap in the 'breeze', and this was
being detected as movement by the room sensor which then activated the
alarm as it was supposed to do. Entirely obvious with hindsight.

The alarm technician said that at this time of year they usually
receive quite a few call-outs to false alarms caused by the heat rising
from radiators and causing decorations to move.

We've now repositioned the ribbons with cards to another wall which has
no radiator underneath.

Others in this NG might care to take note. Happy Christmas.

--
David C.Chapman - )
--------------------------------------------------------------------------