Medical devices include instruments, machines or implants used in medical care. Some, like X-ray machines or thermometers, diagnose diseases or conditions. Others, like pacemakers or inhalers, are used for prevention or treatment. In the U.S., the government's Food and Drug Administration (FDA) must approve any device before it can be sold. The FDA also monitors safety for approved devices. If a device is defective or causes a health risk, the FDA can issue a recall. If you use a medical device at home, make sure that you understand how to use it and follow the directions carefully.