Smartphones have evolved into all-purpose computing machines with exceptional capabilities. They are becoming increasingly powerful, with modern audio "codec" (coder/decoder) chips that provide recorded audio of high quality. Smartphone developers now offer many sound applications (apps) using both the devices' built-in microphone and headphones. This, in principle, enables hearing tests like pure-tone audiometry on a smartphone, where students can measure the frequency-dependent hearing threshold level of their own ears using a smartphone. They may test each ear individually and compare them, or compare their results with others. Experiments on this physiological subject provide an opportunity to understand and deepen many physical concepts in an interdisciplinary approach.