21 CFR §892.1180

1. (a)Identification. A bone sonometer is a device that transmits ultrasound energy into the human body to measure acoustic properties of bone that indicate overall bone health and fracture risk. The primary components of the device are a voltage generator, a transmitting transducer, a receiving transducer, and hardware and software for reception and processing of the received ultrasonic signal.
2. (b)Classification. Class II (special controls). The special control for this device is FDA's “Guidance for Industry and FDA Staff; Class II Special Controls Guidance Document: Bone Sonometers.” See § 892.1(e) for the availability of this guidance document.