End-of-train device

[1] They originated in North America, and are also used elsewhere in the world, where they may include complete End of Train Air System (ETAS) or Sense and Brake Unit (SBU) devices.

A "dumb" ETD can be as simple as a red flag attached to the coupler on the last car of the train, whereas "smart" devices monitor functions such as brake line pressure and accidental separation of the train using a motion sensor, functions that were previously monitored by a crew in the caboose.

[1] The ETD transmits data via a telemetry link to the Head-of-Train Device (HTD) in the locomotive, known colloquially among railroaders as a "Wilma,"[where?]

A typical HTD contains several lights indicating telemetry status and rear end movement, along with a digital readout of the brake line pressure from the ETD.

Railroads have strict government-approved air brake testing procedures for various circumstances when assembling trains or switching out cars en route.

In most cases, the engineer is able to use information from the ETD to verify that the air pressure reduces and increases at the rear of the train accordingly, indicating proper brake pipe continuity.

Some roads still use cabooses where the train must be backed up, on short local runs,[1] as rolling offices, or railroad police stations and as transportation for right-of-way maintenance crews.

As their use became more widespread through the 1980s, ETDs were equipped with radio telemetry transmitters to send brake pressure data to a receiver in the locomotive.

Later models have a small turbine-powered electrical generator using air pressure from the brake line to power the ETD's radio and sensors.

In some cases when working entirely within one block section, an 'LV' sign is not needed if the number of coaches or wagons is communicated by telephone to the next station.