Pass of Brander stone signals

They are part of a warning system that advises train drivers to exercise caution in the event of a rock-fall, and cover a section of track that is just over 4 miles (6.4 km) in length.

In the event of one or more wires being broken, signals in each direction will automatically fall to the 'danger' position, thus providing advance warning to train crews about possible rocks on the track ahead and/or other damage caused by rockfalls.

In response, the secretary of the C&OR, John Anderson, devised a system that would detect falling rocks and provide a warning to drivers.

[1] The name 'Anderson's Piano', derives from the inventor of the signals and the humming noise that the tensioned screen wires are said to make in the wind.

[1][2] Although trip wires working with colour light signals are occasionally used alongside railways in the vicinity of airports, and are common in railroads running through the Rocky Mountains and similar areas around the world, the Pass of Brander system is much older and entirely mechanical in operation.