Here's an interesting game: Chicago Coin, a manufacturer with a terrible reputation (that I have not been able to fathom), created this game that automatically sensed a special 'golden ball' for double scoring.
This is fascinating for a couple of reasons:
1) There are no special mechanisms that I can see to sense the gold ball from the IPDB photos
2) It used a credit projection unit, which, though common for the time in Gottlieb games, was unusual to find in other games.
The game has gorgeous Roy Parker artwork as well.
