"Wau Wau" pit telephone

The "Wau Wau" was used to transmit information to a certain area of the mine over multiple speakers at the same time. The name of the device corresponds to the noise that was made when turning the coil attached to the listener. This noise is similar to the bark of a dog and is the reason why the name "Wau Wau" rapidly caught on. The miner can transmit information selectively through a stipulated sequence of noises.