DSC Alarm Details

DSC Alarm Details

I’ve had a couple of requests for more details of the security system. It seems a few people were intrigued by the mixture of wired and wireless sensors on the system.

The main drawback with wireless PIRs is that they all feature some kind of high traffic shut-down feature. This is purely to limit the drain on the battery, and means that after each ‘activation’ of the sensor, the unit powers down and will not transmit any more detections for 3-4 minutes.There is usually a lag of about 5 seconds before it reports the detection in the first place too. This is apparently to allow time for any door contacts to signal their own violation before the PIR does, so that entry delays etc work as intended.

Basically, the layout of the house made it reasonably easy to get cables to each room on the ground floor: garage, hall and open plan kitchen/living room. Each of these areas being fairly high priority for various reasons:

The Hall This would clearly need a good, reliable contact on the front door, as this would be the only ‘Delay’ zone in the whole system. It is also where the only keypad is mounted, so the area needs to be covered by a PIR too

The Garage This seems to me to be the weakest point in the security of the house. If someone manages to force the main garage door (not very difficult to do!) they can then close it behind themselves and set about using my tools to cut through the internal door that leads into the house with little fear of discovery.

An added vulnerability is that this was where I was going to mount the secondary cabinet with the 8 zone expander in, so I wanted to cut down the amount of time someone would have to open that up and fiddle about inside.

So I’ve got a big ‘garage door’ type contact on the garage door, a contact on the door into the house and a Dual Tech PIR watching the whole space. Dual Tech as there’s quite a lot of temperature variation when the sun hits the metal garage door. The whole thing heats up like a radiator

The Kitchen/Living Room This occupies the whole of the back half of the house and the back wall is practically all glass. So a Dual Tech seemed to be the only way of covering this while avoiding false alarms from bushes blowing around outside the windows.


The upper floors were much simpler, and PIRs could be mounted on the outside walls, facing in. This would hopefully rule out any false alarms due to sunlight through the windows. And all of the doors and windows have wireless ‘disappearing’ contacts installed. I love these little things. They fit in-between the window and the frame, so are completely hidden when the door or window is closed.