On Mon, 21 May 2012 15:37:41 +0100, Terry Pinnell
wrote:

I've just removed the alarm reed relay sensor from the frame of my front
door because it's become unreliable, often 'sticking' in its passive state
instead of triggering the alarm. But I now face some ambiguity about
ordering a replacement, because none of those I've found, like these

http://cpc.farnell.com/elmdene/4bp/4...ont/dp/SR02970

actually specify whether the contacts are NO or NC. And the phrase itself
appears to mean different things to different people!

Stop right there. That is a managed sensor. Replace in kind only. Look
up make and model and then find an "acceptable" substitutes list if you
cannot find an exact replacement.

Will now read the rest of the thread.

?-)