Abstract: Perfect failure detectors can correctly decide whether a computer is crashed. However, it is impossible to implement a perfect failure detector in purely asynchronous systems. We show how to enforce perfect failure detection in timed distributed systems with hardware watchdogs. The two main system model assumptions are (1) each computer can measure time intervals with a known maximum error, and (2) each computer has a watchdog that crashes the computer unless the watchdog is periodically updated. We have implemented a system that satisfies both assumptions using a combination of off-the-shelf software and hardware.