Unexpected Christmas problem with alarm system.

[David Chapman]

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.

[Graham.]

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

[Andrew Gabriel]

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

[Mike Tomlinson]

In article , Andrew Gabriel writes

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.

[Brian Gaff]

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

Brian

[Stephen H]

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

[dennis]

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.

[Andrew Gabriel]

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.

[Mike Tomlinson]

En el artículo , Stephen H escribió:

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.

[fred]

In article , Mike Tomlinson writes

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.

[Jeremy Nicoll - news posts]

I'd have thought that might tempt passing scrotes to kick the door for the hell of it... which would surely piss off the neighbours pretty quickly.

[Huge]

Correct.

[fred]

This assumes that the presence of the device is advertised.

Also, the device is adjustable and the intention is to set the sensitivity such that very significant blows are required to trigger it. On the risk of potential nuisance triggering, if someone is kicking the shit out of my door I want people to know about it before it turns to splinters.