mbyron wroteThe case play refers to the clock reading 0 minutes and 00 seconds, which does not take tenths into account. The clock could have been stopped with time remaining, which would explain why the horn hadn't sounded.
Make sure that the clock operator has the automatic horn on. If the automatic horn is off, then the buzzer won't sound. In thirty years I've had the 0:00 situation with no horn several times. I always ask the clock operator, "Is the automatic horn on?" If he replies, "No", I ask him to turn it on. In many, but not all cases, the horn sounds, so we don't line up rebounders for the free throw. In a couple of cases the horn didn't sound when the automatic horn was turned on, so we had the rebounders line up during the free throws.