A single-station real-time earthquake detector has been developed which operates in the frequency domain. Frequency domain operation is possible because the method of calculation of the discrete Fourier transform and the data format have been adapted to suit the architecture of the microprocessor used. A test period of 10 days resulted in a detection reliability of greater than 95 per cent, with a false detection rate of less than 10 per cent (241 earthquakes total sample). The spectral detector outperforms time domain detectors in two respects. It is much more likely to identify the more distant, emergent earthquakes, and those recorded with a low signal-to-noise ratio. The algorithm operates on a Motorola MC6809 microprocessor and uses less than a quarter of the available time at a 50-Hz sampling frequency.