A continuous glucose monitoring system (CGMS) is an FDA-approved device that records blood sugar levels throughout the day and night. There are a number of technologies that are being tested but the only approved device, Medtronic's MiniMed device, can provide up to 288 glucose measurements every 24 hours. The system is used to measure an average blood sugar for up to 3 days, while the person with diabetes continues daily activities at home. A tiny glucose-sensing device called a "sensor" is inserted just under the skin of your abdomen. The insertion is quick, and is usually not painful. The sensor measures the level of glucose in the tissue every 10 seconds and sends the information via a wire to a pager-sized device called a "monitor" that you attach to a belt or the waistline of your pants. The system automatically records an average glucose value every 5 minutes for up to 72 hours.
CGMS is, however, not intended for day-to-day monitoring or long-term self-care and it is not a replacement for standard blood sugar monitoring. It is only intended as diagnostic tool to discover trends in glucose levels. This helps your health care team make the most appropriate decisions regarding your treatment plan.
After 3 days, the sensor is removed at the doctor's office and the information stored in the CGMS is downloaded into a computer, where you and your doctor or diabetes health care team can then review your blood sugar levels in relation to the other data collected and make any necessary adjustments in your diabetes management plan.
To answer your question, yes there is a machine that will constantly monitor blood glucose readings, however it is used as diagnostic tool only. Even then, you still have to calibrate the machine by using fingerstick blood glucose reading. Hopefully though, in the next 5 years, we will see a breakthrough in diabetes technology.