On Wed, 26 Jan 2005, Dave VanHorn wrote:

> I can't say that I have NOT seen an active beam-break system used, but 
> they are rare. Most common, is doppler microwave, followed by passive 
> IR.

It's not beam-break, it's reflective. Send modulated IR, receive same 
(using sensor in the same box usually). If the reflectivity of the 
target changes significantly (either way!) for a certain amount of time 
open the door.

Peter
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