This interesting little wall mounted device was pictured in 1983 at Caldergrove House, just before the house was demolished.

This is a wall mounted “speaking device”. Becoming popular in Victorian households, they were all the rage in the 1870s. They were used right into the 20th Century, a predecessor of a house phone.

At mouth level, this was situated on a wall on the first floor landing and was an early communication device, most likely directly linked to servants quarters or the basement kitchen. Switches would change the direction of the internal plumbed tubing so that voices could be directed to upper or lower floors.

A normal installation had a removable whistle plugged into each end. To initiate a conversation Person A removed his whistle and blew down the tube, sounding the whistle at the other end. Person B then removed his whistle, and talking could begin. Hence the expression, still current in Britain, “I’ll get him on the blower” when a telephone call is meant.
Such systems appear to have been quite common in homes and offices, though very little information about them, and very few references to them, seem to remain today.

This device would have been especially useful to contact the domestic house servants.