These measure temperature, light levels, pressure, humidity and
many other analogue events in the real world. These can then trigger processes and the appropriate output action as required. For example, if a thermistor (temperature sensor) reading is higher than 23°C, the computer could signal motors to open the greenhouse windows .Sensors are also used to track eye movement or head movement to allow disabled people to use
computers. Eye and head movements operate a pointer on the screen, instead of using a mouse.