Personal assistants who know all of your business might be fine in the halls of Downton Abbey or stately Wayne Manor, but there’s something a bit unsettling about their 21st century equivalents, smart watches. Chalk it up to working-class roots or incipient techno-paranoia, but many of us balk at a networked device that tracks our every habit, secret and preference like a cybernetic Mrs. O’Brien, particularly one built by a company with a burgeoning robot army and a secretive barge flotilla. Then again, they’re kind of cool…