[NetBehaviour] Light Beams Guide Blind Thru Building Without Escort (Jul, 1934).

[marc garrett]

Light Beams Guide Blind Thru Building Without Escort (Jul, 1934).

"BEAMS of light now guide the sightless through building corridors and 
up and down stairways. The subject is equipped with a portable photronic 
cell unit which sounds a buzzer as long as the operator travels along 
the light beam. The buzzing ceases when the course is changed."

Source: Modern Mechanix
http://tinyurl.com/3rd79e