RailRoad Sound bomb signal

Hi, I’m new to the forum. I was wondering about a story my grand father told me many years ago.. when he was a kid, he said he stole «*sound bombs*» that they used on the railway to alert the driver of a passing train of a danger or something of the kind. He said he detonated them in the center of the city... Do some of you know about those? I searched the internet and have not found anything. He obviously knew what he was talking about because he worked for the CN all his life and he stole the bombs from his fathers casing, (who also worked for the CN all his life). Thanks!