What I need to know is how the "electronic eyes" work. Do they send a
signal back to the opener ? Are they just a voltage loop that is opened
when something crosses the beam ? I believe thay are powered by DC
voltage.

The reason I ask is I am trying to build a timing clock for a guy and his
soap box derby car, and he got a pair of sensors for us to use and timing
spots to start and stop the digital stop watch, I need to build.