How to fit door contacts / PIR for house alarm

[darbo1103]

I am in the process of having a conservatory built and need to wire the doors to the house alarm. Can I fit the door contacts in series with the ones already on the french doors or do they need to be wired separately. Also, is it also possible to fit a PIR in the conservatory and how do I wire this into the system? The actual house alarm it quite far away from the site and I would like to know how to run the wires. I can't get under the house floor as it has laminate flooring.

[buildersmate]

Here's a tangential thought for you - have you asked yourself why you actually want the alarm extended in to the conservatory?
If you have a decent external lock on the door and the alarm goes off anyway when the burglar moves from conservatory into the next room (often the lounge) and you aren't in the habit of storing the wife's diamond tiara in the conservatory, what's the problem?
I'm only suggesting this because what are wanting to do IS a pain in the arris to wire up.

[darbo1103]

Mmm, can see your point, but we have a flat screen TV on the wall and iPod dock in the conservatory, so Billy Burglar may not enter the rest of the house. We will have decent locks, internal beading,close the blinds so nobody can see in, etc, etc, but I would still like the security of having the alarm extended to cover this area.

[buildersmate]

OK then, I see your reasoning.
It is probably possible to wire up an additional sensor in series. But you need to get hold of the Installation Manual. With my system, there are 6 wires going to each sensor (either contacts or PIR). One pair is the actual contact, the second pair is a closed loop with about a 20k ohm resistor in the sensor. This passes a very small current continuously and is the method by which the 'Tamper' circuit works. If Billy Burglar cuts the wires, the control knows it has been tampered with and all hell breaks loose.
I think that most commercial systems are similar.
The third pair, by the way, provides a 12v power supply to the PIR units (it is not used with the contacts).
6 core cable isn't very fat because the individual wires are so thin - about the same as a telephone cable - but you have to either route it through or round the outside of the house. No other way - sorry.
I guess this is why ther'e a ready market for wireless systems for retrofitting in domestic properties that lack the wiring when the house was built.

[darbo1103]

Buildersmate - Thanks for the advice, I'll take a look and see what I can do with the system I've got.

[woodchopper]

In addition to what bukidersmate has said - If you are going to install a PIR I would be inclined to fit a sensor that has temperature compensation in-built, especially if it is in a conservatory. Personally I dont see the point in a set of door contacts when a perfectly good Dual Tec ( better than PIR ) sensor correctly positioned will do the same job. As soon as Bertie the burglar sticks his neb in through an open window or door it will trip.