Bell or ringer is one of the most used tools in the food and beverage industry.
In some places with a bigger seating capacity, they might use a “walkie talkie” to let the kitchen know that the food is ready to be served.
There are also different types of a ringer, it can be electronic or just like the photo above which is mechanical like the bell.
You might heard it often when you set the alarm clock on your phones, make sure you are not alerted because you have to serve a hot dish to a table. 🙂