[pizza]

Well, resolution for fingerprint scanners is roughly 500 dpi [0]; 1 in^2 = 645 mm^2; so.. maybe, I'm not sure!

But, that said, I believe there are many >1 mm^2 resolution features that can basically uniquely identify users, like, the shape of a hand (individual finger geometry, etc), the length of a limb, the particular subcutaneous layout of veins, face geometry, etc. It's interesting to ponder about, at least!

Currently looking around for cheap (and arduino-amenable) single chip radar systems whereby I might try to hack together a more low tech prototype of Soli

[0] http://www.neurotechnology.com/cgi-bin/fingerprint-scanners....

[shostack]

Or even a special carved ring, or sticker or something.