"John Fields" wrote in message
...
On 10 Nov 2005 14:40:39 -0800, "bhauth" wrote:

Well, you *can* use optical means: bright infrared LEDs, infrared
markings, and an infrared-filtered CCD, for example. Magnetic sensing
is just better.

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Didn't you bother to read the thread?

It's _implanted_.

Only 10mm deep though. Try shining a torch through your hand. I'm sure I
read that someone was trying to use light to replace some hospital x-rays.
They were experimenting with using sensitive sensors similar to those used
by optical telescopes. Probably wouldn't work for this application but it
might not as daft as you imply.