SdrTuner Supports HackRF / RTL-SDR on Android phone/tablet and this app will visualize the RF spectrum (frequency magnitude and waterfall plot)!
Browse through the frequency spectrum just by using scroll and zoom touch gestures.
Or use buttons to change frequency with step drop boxes at the bottom. You can reach high or low frequencies easily by this buttons.

Features are:
- FFT size, averaging, peak holding, color scheme, ...
- Read samples from a file (generated by hackrf_transfer tool or by rtl_sdr)
- AM/FM/SSB/WFM audio demodulation
- Adjust squelch and channel width
- Record to a raw IQ file compatible with hackrf_transfer, ...

In order to use this app you will need:
- A HackRF or an RTL-SDR dongle (about 8$)
- An Android device that either supports USB OTG or has an USB host port