Yes, I'd heard/read something like that. There are limited-range systems, though. WalMart is able to inventory their stock quite precisely from a cart-mounted unit that they just drive/push down the aisle. That way they don't end up with an oversupply of 30" waist, 40" inseam pants. They couldn't do that from just a few feet. I'm going to have to learn some more about those, as I recall a national news broadcast indicating that they could work from as far as 60 meters. I found that rather disturbing. I don't want a stranger able to find out my waist and inseam without first introducing himself.

What I was thinking, regarding the cheap ones, was that I could use those ultra-cheap units that just transmit "it's me, nnnnnnnnnnnnnnnnnnnnnnnn" where n is a hex digit. I would use one for each sensor. Maybe that's not a reasonble way, since it has to be able to perform randomly, or at a high enough rate to cover all the sensors within range in, say, 1/30 second. They wouldn't have to respond, of course, unless they had something to say.

<sigh> I'd hoped this would be easier to figure out.

RE