Human: I've heard that some people use a stethoscope to check their babies' heartbeats. How does it work? Assistant: 
Stethoscopes are acoustic devices used by medical professionals to listen to the heart and lungs of patients. They consist of a chest piece, which is placed on the patient's chest, and a headpiece, which is held against the patient's body. The chest piece contains a diaphragm that vibrates in response to sound waves from the patient's body. This vibration is then transmitted through the headpiece to the listener's ears, allowing them to hear the patient's heart and lungs.