On 03/09/2012 18:47, charles wrote:
In article ,
....
more likely the magnet is an electromagnet which loses its power when then
fire alarm goes off. I suspect the High temp ones would be far too late -
the door itself could well be on fire by then.


I would be more concerned that it was doing nothing to stop the spread
of smoke so long as it stayed open.

Colin Bignell