Re: prior art?
Indeed, I'm shocked that this has been granted (although not shocked when considering other things granted in the past!).
I wouldn't expect this to survive a challenge, except perhaps on very specific narrow claims that are buried in the patent somewhere but don't leap out at all as obvious.
There are claims for:
a) eye-tracking (used in military pilot HUDs, IIRC)
b) facial expression tracking (an obvious extension?)
c) body tracking of whatever is in field of view of device (as per (b))
d) local environment sensors (duh, in a phone)
e) authentication methods (hat won't work for everyone, but phones do this so prior art should cover this)
f) Notifications (isn't that what a HUD is partly for?)
g) neural input sensors in the hat (probably lots of prior art for that)
h) bone conduction output for audio (exists already)
i) computing power in the hat structure to deal with all these sensors (duh)
j) flip-away display (obvious extension to existing stuff)
Can't be arsed to read further into the detail beyond the claims.