On Mon, 28 May 2012 23:32:09 +0100, Jim K wrote:

As used with intruder alarm systems. Many to choose from...

including ones rated for exterior usage?

I don't recall "exterior" being in the spec. B-)

precisement - which "some" are those though?

An excerise for the readers googlabilty, one source:

http://www.gjd.co.uk/products/wired-detectors/

But you probably aren't going to like the price...

--
Cheers
Dave.