You could expand the forward sensor to multiples, for doorways or people, say; have a few, say, 5, or 3 at different horizontal forward angles, with correspondi

You could expand the forward sensor to multiples, for doorways or people, say; have a few, say, 5, or 3 at different horizontal forward angles, with corresponding vibrators or a sequence of audible beeps (low, non-annoying when nothing is present). The user would learn to map these vibrations / beeps to the real world, as shown by that guy with the belt of cellphone buzzers a couple of years ago.