Conventional frequency-modulation (FM) detectors show a marked decrease in outputS/Nbelow an inputS/Nof 5 to 10 dB. This threshold effect is caused by "clicks" or phase slips of multiples of π. This effect is related to a normalization (clipping) which is very beneficial at highS/N. A detector is described which has no normalization and is superior to the ideal detector below zero to 10 dB inputS/N. The noise at the output of the detector is additive for all inputS/Nratios and in this sense is comparable to synchronous detection of AM. Plots of output noise spectrum and outputS/Nwith and without sine-wave modulation are given. Another detector is also proposed that is asymptotic to the ideal detector at highS/Nand the aforementioned detector at lowS/N. Comparison is made with conventional detectors. The results indicate that this detector may be especially useful in the detection of frequency-shift keying and phase-shift keying in telemetry systems.