A derailment detector for a railway vehicle includes a housing in selective fluid communication with a brake pipe of the railway vehicle to receive compressed air from a pneumatic braking system. A main chamber is disposed within the housing and pressurized by the compressed air. A shock detection assembly is adapted for detecting an acceleration indicative of a derailment condition and activating a main valve disposed within the main chamber upon detection of the acceleration indicative of the derailment condition. A discharge valve is in selective fluid communication with the main chamber, where, upon detection of the acceleration indicative of the derailment condition, the discharge valve is operative for discharging a predetermined amount of the compressed air from the main chamber to indicate that the derailment condition has occurred.