Embedded micros (Systems On a Chip) often include dedicated watchdog hardware. This is a timer which is reset ("fed") by writing values to a specific register. Crucially, it often isn't just one value; you have to alternate between two values. That way, you can write one value at one point in your event loop and the other value at another point, making it less likely that something will break but keep feeding the watchdog.

If the watchdog hasn't been fed for X milliseconds, then it resets the system.