Hooter (noun)

1. A horn or whistle, especially one used as a signal on a train or ship.
2. A device that makes a loud noise, such as an alarm.

Origin:

The word hooter is of uncertain origin, but it has been in use since the early 19th century. it likely comes from the onomatopoeic sound that a horn or whistle makes.

Examples:

1. She pressed the hooter to get the driver's attention.
2. The hooter went off and everyone jumped.
3. He blew the hooter to signal the start of the race.
4. The hooter sounded and the game began.
5. I heard a hooter and I knew it was time to go.