By its broadest definition, a sensor is a device, module, machine, or subsystem that detects an event or change in the environment and sends that information to another electronic device (often a computer processor). Sensors are always used in other electronic devices.
Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensors), lamps that darken or brighten when touched by the base, or in a myriad of applications that most people don't notice. Advances in micromachines and easy-to-use microcontroller platforms have expanded the use of sensors beyond the traditional domain of temperature, pressure, and flow measurement.