A vibratory PEP respiratory therapy device (100) includes a valve element (11) on a rocker arm (12) that opens and closes an opening (10) during exhalation through the apparatus. An accelerometer (20) including a piezoelectric beam (22) supported at one end (23) is mounted on the outside of the housing (2) of the device to respond to vibration transmitted though the housing caused by oscillating movement of the rocker arm (12). The output of the accelerometer (20) is supplied to a circuit (28), (29) that determines when the device (100) is used and the duration and quality of use of the device.