This was available in some (probably limited and gimmicky) form decades ago in devices like the Reflection Technology Private Eye. This is the best link I could

This was available in some (probably limited and gimmicky) form decades ago in devices like the Reflection Technology Private Eye. This is the best link I could find: http://www.loper-os.org/vintage/paralleleye/eye.html http://www.loper-os.org/vintage/paralleleye/eye.html ... I think it was in Hackers, so you know it's good.