And there isn't really any technical reason why Glass (or successor technologies) couldn't just record constantly, eg. continually overwriting a buffer of the last 60 minutes, the same way dashboard cams do. If you happen to see something interesting, just look at it, and then afterwards instruct Glass not to delete it.
There are already dedicated personal video recording devices that can do this. When you're just recording video (and not doing any other functions) it's easier to extend battery life, etc.
Wait, how do you wear that? Does it go over ear or something?
Of course, there are cheaper and more discrete solutions, like this one [1], the one you linked is probably even more conspicuous than Glass, and half-VGA resolution is pretty bad. I use the linked one as cheap motocycle cam, and it is hard to aim properly with no viewfinder, but what you can expect for about $ 10.
I don't know if it's more conspicuous than glass - it's very similar to a lot of bluetooth headsets. And it's been out on the market for a long time with hardly any controversy.
There's lots of devices like this - I also remember some systems that cops wear that just clips onto the front of your shirt and looks kind of like a pager. Glass isn't particularly novel in this regard (except for maybe its connectivity via wifi).
As of today, yeah it'd eat your battery alive. However, unlike something that spins a motor or shines a light the essential work involved may be low enough that even without advancements in battery technology it may become feasible or even trivial.
