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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorRex
    • CommentTimeJan 8th 2020
    What ho one and all,

    Like may, I have PIR sensors scattered around the house to activate the alarm. They all have a 'Pet' option so as not to activate if/when the dog/cat wanders past.

    It is my understanding that they are activated by heat and movement of that heat source.

    I also have some PIR sensors outside to turn the garage and front door lights on. These do not have any 'pet' option, only ambient brightness and time. But they come on/off throughout the night just by some nearby shrubs and bushes swinging in the wind. Apart from annoying me and the neighbours, it is also using electricity for no reason.

    Re-siting the bush is not an option; re-siting the sensor is possible but challenging. Since a bush is not emitting much (any) real heat, why do the sensors pick up the movement so readily and is there a kinda interior version option for the external sensors?

    Thanks and toodle pip

    • CommentTimeJan 8th 2020
    Don't know why PIR sensors pick up bushes, but ours do it too. I suppose the sensors are sensitive to reflected IR as well as emitted, so perhaps bushes are good at reflecting whatever IR is around from the sky or house etc.

    We tend to regard our outdoor ones coming on spuriously as a good thing. It lets us and any potential burglars know they are there and sensitive. Maybe you can adjust the lights so they don't shine at the neighbour?
    • CommentAuthorRex
    • CommentTimeJan 8th 2020
    Unfortunately not; they are mounted on the wall and although do not directly shine at the neighbour, they do provide night-time illumination to the back of his house.

    The other 'trivial' issue I have is that all these PIR are made from plastic which has a limited life when in direct sunlight. The dome on two of them is starting to disintegrate. Spoke with the manufacturer today they basically told me where to go!!!! So much for good customer relations.
    • CommentAuthorMike1
    • CommentTimeJan 12th 2020
    You can get 'dual technology' (PIR + microwave) motion sensors for intruder alarms that only trigger if both technologies detect something. There must be external versions, and no doubt they could be adapted for lighting...
    Have a look at


    may help, or do a google search for more pet friendly sensors
    • CommentAuthorRex
    • CommentTimeJan 17th 2020
    What ho Peter,

    Interesting and thanks for the link.

    The current PIR is wired into the mains so not sure how this one, which has batteries on-boards, would activate the lights.
    • CommentAuthorHoveTom
    • CommentTimeJan 25th 2020

    As I’m nearing the end of a renovation I’ve been looking for external lights with this option too but to no avail. It’s seems very difficult to find any. I have a lot of foxes which love to sit around in my garden all night and the last thing I or my neighbours want is night lights coming on and off all night.

    I’ve been told Stienel make about the best external lights (within sensible reason) and they do a separate sensor which is very adjustable but it is pricey and it depends on your present wiring. I’m considering their traditional L15 lantern type light which has a directionally adjustable sensor so that you can aim its arc of view slightly. This may be enough for you to avoid a certain bush or adjust it over the height of a running fox.

    Worth a look and hope that helps.
    • CommentAuthorborpin
    • CommentTimeJan 26th 2020
    I've got an LED light with a microwave as opposed to a PIR sensor. There is a bush opposite and I have not noticed false detection.


    Currently on offer via code (see main page)
    • CommentTimeJan 26th 2020
    I would have thought a microwave sensor suffered from more false positives, since it can't tell a live moving object from a dead one (loosely speaking), so a combined sensor is often viewed as best?
    • CommentAuthorMatBlack
    • CommentTimeJan 26th 2020
    Do the PIRs have an almost bug eye, multi face plastic bit? something moving across different sections of these can activate the pir. If so can you cover a couple of sections ( facing bushes) with some tape?
    • CommentAuthorCWatters
    • CommentTimeJan 26th 2020 edited
    Re:The other 'trivial' issue I have is that all these PIR are made from plastic which has a limited life when in direct sunlight.

    I don't think PIR should be located in direct sunlight. I recall reading that sunlight can cause changing air currents inside the PIR sensor leading to false triggering.
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