But remember, it was a Jack Webb production and he was a stickler for realism.Before another local agency took over our fire department, I had two tone set up for our station alerting.
During the day time, the radio was set so that all traffic was heard through the speakers, including the two tone alert.
At night, they'd switch to a second channel that had everything but their tones muted.
So, yes, depending on how they were set up, the could have heard the tones during the day.
But, it's TV and anything goes on TV, even if it doesn't make sense.