An event recorder is a device which records information which can be used in the analysis of an event. Event recorders are used in a variety of settings, from assessments of cardiac patients to the investigation of accidents involving aircraft. Some people may use the term “event recorder” to refer specifically to a railway event recorder, a device installed in trains which operates much like the flight data recorder or “black box” used in aircraft.
Since the information in an event recorder may be used in a legal investigation, a court of law, or a patient's medical treatment, in the case of Holter monitors worn by cardiac patients, the device needs to be highly accurate. It also needs to resist tampering. Transportation event recorders like those used in ships, planes, and trains are designed in such a way that it is very difficult to alter the information stored in the recorder, and when information is altered, it is easy to detect the signs of alterations.
A typical transportation event recorder collects an assortment of data including speed, direction of travel, and altitude, in the case of aircraft. The event recorder also monitors electrical and communications systems, takes notes of commands recently entered into the system and the system's responses to those commands, and may also record audio from operators. The storage method varies, depending on the company which makes the recorder, and event recorders may be designed to overwrite old data, or the data may be stored until it is removed.
One of the classic uses of a transportation event recorder is in the investigation of an incident or accident. The event recorder is an impartial and highly reliable witness which can provide a great deal of information to investigators about the circumstances surrounding the event, the actions taken by people involved, and what happened during the event. Event recorders can be used to uncover signs of negligence or improper operation, or to reveal that an accident was genuinely an accident, caused by something like a freak occurrence which disabled the systems on the train, aircraft, or boat.
Event recorders are also sometimes used in employee assessments, to monitor employees, or in ongoing investigations of employees who are believed to be negligent. For example, a subway authority might use event recorders to demonstrate that drivers are not operating trains in accordance with company policy and safety regulations, using this data to retrain problem employees or to fire employees who have already been warned about their activities on the job.