Sensors are physical probes that check the health and status of hardware. Manufacturers have put more and more sensors in hardware, providing low-level hardware information to the operating systems. OpenBSD supports a wide variety of hardware sensors, and uses the
sensorsd daemon to query them and act upon error states.
Resolving many hardware errors requires shutting down the machine, but advance warning that a component has stopped working changes a hardware failure from an unexpected middle-of-the-day catastrophe to an after-hours annoyance. Some hardware, such as hot-swappable hard drives, can be replaced without interrupting service once you know the hardware has failed.
Each physical sensor has a device ...