We present here physics lessons on the application of the simple oscillation concept through measuring the rate of human respiration during various activities. The measurement used a smartphone’s magnetometer sensor, which recorded changes in the magnetic field of a permanent magnet that was attached to the stomach while breathing. Measurements were taken during rest, after walking for 10 min, and after running for 10 min. The experimental results showed that the magnetic field changed periodically with respiration, which indicated an oscillation. From the recorded magnetic field data, the oscillation period and respiratory rate per minute were calculated. From this experiment, physics students can learn that human breathing is an application of the concept of oscillation because it is periodic. This method is also an alternative to the conventional method using a stopwatch. Students also learn how activity affects the rate of breathing.