A medical device comprises a surface, an ultrasonic sensor, and a processor. The surface is configured to interact with skin of a patient during operation of the medical device. The ultrasonic sensor is disposed beneath the surface and configured to ultrasonically measure data with respect to a region above the surface. The processor is coupled with the ultrasonic sensor. Responsive to detection of a finger in contact with the surface, the processor is configured to operate the ultrasonic sensor to capture a fingerprint of the finger. Responsive to authentication that a person associated with the captured fingerprint is authorized to use the medical device, the processor is configured to activate operation of the medical device.