Abstract: A clock monitor circuit detects departures from expected values for clock period, clock high time duration, or clock low time duration. A delay line of the clock monitor circuit is composed of delay portions of delay cells. Each delay cell also has a comparator portion with logic to compare aspects of the monitored clock signal to corresponding expected values, and to output a failure detection signal indicating whether the expected values are met. Expected values may be read from a fuse set. The delay of the delay line may be programmatically adjusted. The clock monitor circuit may be combined with a circuit that detects narrow glitches in the monitored clock signal. Devices and systems with one or more monitored clock signals, and methods of clock signal monitoring, are also described.