Telemetry is a technical, generic term for remote tracking data.
The term is perhaps most commonly associated with spacecraft. Data is more or less continually being transmitted back to earth reporting on the craft’s position, condition, and activities. This data is referred to as telemetry.
In the computer world, the same term can apply to any data being used to remotely monitor the condition or activities of a computer. Regardless of the level of detail – from minor and anonymous error reports to deeply detailed activity logs – data sent back from computers to a central location for purposes of reporting or monitoring is also referred to as telemetry.
Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots tele, "remote", and metron, "measure". Systems that need external instructions and data to operate require the counterpart of telemetry, telecommand.
Although the term commonly refers to wireless data transfer mechanisms (e.g., using radio, ultrasonic, or infrared systems), it also encompasses data transferred over other media such as a telephone or computer network, optical link or other wired communications like power line carriers. Many modern telemetry systems take advantage of the low cost and ubiquity of GSM networks by using SMS to receive and transmit telemetry data.
A telemeter is a physical device used in telemetry. It consists of a sensor, a transmission path, and a display, recording, or control device. Electronic devices are widely used in telemetry and can be wireless or hard-wired, analog or digital. Other technologies are also possible, such as mechanical, hydraulic and optical.