A good friend of mine is blind. I think it has not made it to market because it's an over-engineered solution that doesn't solve the problem better. Most blind people would say 'Why the hell would I want a buzzer on a heavy cane?'. It buzzes when I am near a stair (aka all day long). Or it buzzes when it hit a step... like it does now when I hit it!
Great story, neat solution, not market viable.