First base umpires have a pretty tough job. A runner's foot can touch the bag right as the fielder catches the ball, and making an instant and definitive call can be dicey. These days, umpires can double-check close calls using instant slow-motion replay, which cuts down on inherent human error. But in seasons past, umpires had to find other ways to improve their success rate.
Previously, umpiring clinics would test their pupils blindfolded to teach them to rely on their hearing when making a call. This was not some sort of Star Wars-inspired mind trick; umpires really can judge a play based on sound. Sure, in games they keep their eyes open, but learning to listen for the thud of a foot on the bag or the pop of the ball hitting the pocket of the first baseman's glove allows them to make more informed calls—and lets them focus on watching for one while listening for the other.
Because of this practice, it's almost surprising that this 1875 patent for a baseball base with a built-in bell didn't catch on. Inventor John C. O'Neill of St. Louis envisioned a bell that would ring when a runner hit the base:
In place of the bell mechanism, a sounding whistle, electrical connection, or any other suitable enunciating device may be employed, which indicates clearly and positively, without chance of error, the exact moment when the base is touched by the runner, so as to form a very useful and reliable device for base-ball players.
The patent was awarded December 14, 1875 but it seems it never caught on for game use.