Abstract: A missing pulse detector is disclosed in which the absence of a pulse in a variable frequency periodic pulse train is detected and distinguished from a reduction in the pulse repetition rate. Between successive pulse train pulses a first counter counts clock pulses at a first rate and develops a maximum count related to the time duration between successive pulses. This maximum count is maintained by a latch circuit during the next time duration between successive pulses and is compared with the count of a second pulse counter which counts clock pulses during successive pulse train pulses at a second rate normally less than the first incrementing rate. When the count of the second counter exceeds by a predetermined amount the latched count of the first counter, this indicates the occurrence of longer time duration and a count comparator and logic circuit provides an arming output signal.