A Look Back at GlucoWatch: The First Non-Invasive Glucose Monitor

When it was introduced, the GlucoWatch Biographer was a groundbreaking innovation in diabetes care. Approved by the FDA in 2001, it was the first device to offer non-invasive glucose monitoring—no fingersticks required. Designed by Cygnus Inc. and later acquired by insulin pump manufacturer Animas Corporation in 2007, the GlucoWatch aimed to revolutionize how people with diabetes managed their blood sugar levels. Though it’s no longer on the market, its legacy lives on in today’s wearable continuous glucose monitors (CGMs) and Automated Insulin Delivery Systems (AIDs).

How the GlucoWatch Worked

The GlucoWatch used a process called reverse iontophoresis, which involved a gentle electrical current to pull glucose molecules from interstitial fluid through the skin. This glucose was then measured using a replaceable sensor pad known as the AutoSensor. The device provided readings every 10 minutes over 12 hours, resulting in up to 36 potential readings per use.

However, several environmental and physiological factors could interfere. Readings were often skipped due to sweating, movement, cold skin, or temperature fluctuations. In clinical studies, users received an average of 26 out of 36 readings per wear session, with approximately 21% of users receiving fewer than 12 usable readings per session.

Features and User Experience

While not an accurate continuous glucose monitor by today’s standards, the GlucoWatch provided valuable insights into glucose trends. It was handy for identifying after-meal spikes, overnight lows, and morning highs.

Personalized alerts for high and low glucose thresholds
Trend indicators showing the direction of glucose changes
Event markers for meals, insulin, or activity

However, the device had a 3 to 3.5-hour warm-up period, during which it couldn’t be exposed to water. Showering, bathing, or swimming required planning, with users often resorting to plastic wrap to keep the sensor dry.

Accuracy and Limitations

The GlucoWatch required manual calibration with a standard glucose meter, which introduced a margin of error. The FDA cautioned that users should never adjust their insulin dosage based solely on GlucoWatch readings. Single readings can be off by more than 30%, especially during periods of rapid blood sugar fluctuations.

Studies submitted to the FDA included 25,000 hours of use and 19,000 data points. While correlation coefficients were above 88%, the variability remained too high for making decisions based solely on them.

Skin Irritation and Site Rotation

One of the major drawbacks was skin irritation. The mild electrical current could cause redness, itching, or discomfort in many users. Around 80% experienced some skin irritation, and 10% found it intolerable. Rotating the application site and applying mild hydrocortisone cream helped alleviate symptoms for some.

Why GlucoWatch Was Discontinued

In 2007, Animas announced the discontinuation of the GlucoWatch G2 Biographer system, effective July 31 of that year, with support ending in 2008. At the time, the device faced increasing competition from more accurate, implantable, or sensor-based continuous glucose monitors (CGMs) such as Dexcom and Medtronic models.

The Legacy of GlucoWatch

Despite its limitations, the GlucoWatch was a pioneering step in glucose monitoring. It showed that wearable technology could offer more than just snapshots of blood sugar—it could help detect trends and improve safety.

Modern CGMs now offer real-time data, Bluetooth syncing with smartphones, and predictive alerts—features that were only aspirational during the GlucoWatch era. Devices like the Dexcom G7, Freestyle Libre 3, and Eversense E3 have transformed the vision of non-invasive, continuous monitoring into a standard of care.

Where to Learn More

Conclusion

The GlucoWatch may be a relic of the past, but its impact on diabetes technology is lasting. It helped prove that wearable, automated monitoring was possible and laid the groundwork for the advanced continuous glucose monitors (CGMs) used today.