In this paper we investigate the possibilities of narrowband FSK detection using a superregenerative (SR) receiver. Previous SR FM demodulation techniques rely on detecting the amplitude variations caused by the different frequencies involved in FSK modulation. However, this requires relatively high frequency deviations because the frequency response of SR receivers is not very selective. In this paper we take a different approach, exploiting the distinct phase trajectories of FSK modulations resulting from the transmitted data. The well-known fact that the SR oscillator response preserves the phase information of the received signal is successfully exploited to allow the detection of several FSK modulations. These include the special case of MSK, opening the way to applying the SR principle to several communication standards, such as IEEE 802.15.4. The key ideas for symbol synchronization are also presented. Experimental results on a 10 kbit/s proof-of-concept MSK receiver, achieving a sensitivity better than -114 dBm in the HF band, validate the proposed approach.