A watchdog timer is a timer which is used to detect and recover from computer malfunctions. During regular operation the controller regularly restarts the watchdog timer, however if a hardware fault or system error prevents this, the controller will fail to restart the watchdog.

If the controller fails to restart the watchdog the timer will overflow and the watchdog timer with then take corrective measures. The corrective measures a watchdog timer takes are usually to just reboot the controller.

Typically the watchdog timer is implemented on the hardware side as a peripheral, alternatively though it can be implemented as software.