Smart rings currently monitor signals such as heart rate, sleep, skin temperature and blood oxygen. A new experimental device developed at the University of California San Diego goes deeper by analysing chemical information contained in sweat.
Known as CHARM, or the Continuous Health Analyzing Ring Module, the prototype can continuously measure as many as four biomarkers at the same time. Its available sensor configurations cover glucose, ketones, vitamin C, uric acid, lactate and alcohol.
Unlike many experimental sweat sensors, the wearer does not need to exercise or use electrical stimulation to produce a sample. The ring uses a specially designed hydrogel to draw tiny amounts of sweat from the skin continuously, even when the wearer is resting.
The research, published in Nature Communications, could eventually support more detailed monitoring of metabolic health, nutrition and diabetes. However, CHARM remains a research prototype rather than an approved medical device, and considerably more clinical testing will be required before it can guide treatment decisions.
How CHARM Differs From Existing Smart Rings
Commercial smart rings primarily rely on optical, motion and temperature sensors. They can estimate physiological measurements such as heart rate, heart-rate variability, sleep stages, activity and blood oxygen saturation.
Those measurements reveal how the body is behaving, but they do not directly show the molecular changes occurring beneath those responses. CHARM was designed to add that missing biochemical layer.
The ring supports six chemical targets across its sensor options, although it can monitor a maximum of four simultaneously. The researchers chose glucose and ketones because of their importance in metabolism and diabetes management. Lactate can reflect exercise-related metabolic activity, while uric acid is associated with processes relevant to gout and cardiovascular risk. Vitamin C provides information connected with diet and antioxidant intake, and alcohol monitoring can reveal changes following consumption.
According to the UC San Diego announcement, the researchers believe CHARM is the first fully integrated ring designed for continuous daily biochemical monitoring. The device combines sweat extraction, fluid handling, chemical sensors, data-processing electronics, a rechargeable battery and wireless communication inside one wearable structure.
The Ring Collects Sweat Without Exercise
Collecting sweat continuously is one of the greatest challenges facing biochemical wearables. Many earlier devices depend on exercise, warm conditions or iontophoresis, which uses a mild electrical current to stimulate sweat glands.
These approaches can make monitoring inconvenient or intermittent. They may work during a workout but provide limited information while a person is sitting, sleeping or completing ordinary daily tasks.
CHARM instead uses an osmotic hydrogel positioned against the skin. The soft material creates a pressure gradient that passively pulls fluid from beneath the skin’s surface into a small channel. The process is similar to the movement of water through plants and does not require a needle or externally stimulated sweating.
The extracted fluid then moves through a microfluidic channel containing electrochemical sensors. Laboratory testing found that osmotic extraction created a flow rate approximately five to six times higher than natural perspiration alone at the ring site. The researchers also reported that the flow remained consistent across different fingers during ten hours of testing.
Using the finger provides another potential advantage. Fingers contain numerous sweat glands and are already a socially accepted location for a small wearable. A ring can remain less noticeable than a large wrist patch while maintaining close skin contact.
Six Biomarkers Are Available, but Only Four Work at Once
The ring’s complete detection range includes glucose, beta-hydroxybutyrate ketones, ascorbic acid or vitamin C, uric acid, lactate and alcohol. However, the current electronics and electrode arrangement limit simultaneous monitoring to four biomarkers.
The limit exists partly because operating additional electrochemical sensors can create excessive voltage loss between electrodes. Different sensor combinations could therefore be installed according to the intended application.
A diabetes-focused configuration might track glucose and ketones alongside lactate and alcohol. A nutrition-oriented version could instead monitor glucose, vitamin C, uric acid and ketones. The researchers believe the underlying platform could eventually be modified for other biomarkers as suitable sensing chemistry becomes available.
This modular approach is important because a single measurement rarely explains a complete physiological event. A glucose change following a meal may have a different meaning when considered alongside ketone levels, exercise-related lactate or alcohol consumption.
Early Glucose and Ketone Results Were Promising
The researchers tested CHARM in healthy volunteers and an individual with type 1 diabetes. Its glucose measurements were compared with conventional blood testing and commercial continuous glucose monitors, while its ketone readings were compared with commercial blood meters.
The sweat-based glucose trends generally followed the changes observed by the comparison devices. Across the reported experiments, the researchers calculated an overall glucose mean absolute relative difference of approximately 13.72%. Other monitored biomarkers produced correlations between approximately 0.85 and 0.90 with their respective blood profiles.
During one experiment involving a participant with type 1 diabetes, the ring followed glucose and ketone changes after meals, insulin and a ketone drink. The sweat measurements sometimes appeared around 15 to 30 minutes after the corresponding changes in blood, showing that sweat and blood do not always reflect metabolic events at exactly the same moment.
CHARM was also evaluated while participants consumed food, exercised and drank alcohol. These tests were designed to examine whether several overlapping daily events could be separated and monitored rather than studying one carefully isolated biomarker change.
Personal Calibration Remains Necessary
The ring does not simply collect sweat and immediately produce universally accurate blood-equivalent values. Individual physiology, sweat composition, sensor behaviour and environmental conditions can affect the relationship between the electrical sensor response and the concentration displayed to the wearer.
The researchers therefore used personalised calibration factors developed through repeated comparison measurements. These factors convert the sensor’s current response into estimated concentration trends for each individual.
The study found that personalised calibration values remained relatively stable for approximately two months. That could reduce the need for frequent blood-based recalibration, but the paper also notes that deviations may require users to recalibrate using conventional blood strips.
Personal calibration is likely to be one of the major issues facing future commercial development. A general wellness device may only need to display trends, but a medical product used for insulin decisions would require highly dependable numerical accuracy across a diverse population and a wide range of real-world conditions.
A Flexible Battery Powers the Ring for 12 Hours
CHARM weighs approximately 5.1 grams and has an outer diameter of about three centimetres. One half contains the hydrogel, microfluidic channel and chemical sensors, while the other contains its electronics and power system.
A custom flexible zinc-silver oxide battery supplies energy to the sensing and wireless communication components. Testing showed that the system could remain operational for more than 12 hours while measuring four biomarkers and transmitting information to a smartphone.
Twelve hours is sufficient for a daytime study but remains considerably shorter than the multi-day battery life expected from many commercial smart rings. Future versions would need easier charging, replaceable sensing components and longer-duration sweat collection before they could function as everyday consumer products.
The current casing is made from a 3D-printed polymer and is noticeably larger than many mainstream smart rings. Miniaturisation would therefore be another important step toward comfortable, unobtrusive daily wear.
The Prototype Still Has Important Limitations
The researchers acknowledge that CHARM is not yet waterproof enough for routine daily use. A future ring would need to withstand handwashing, rain, exercise and other forms of moisture without allowing water to contaminate the sweat sample or damage its electronics.
The study was also not a large clinical trial. The device has not been comprehensively validated across large groups of people with diabetes or tested throughout the full range of potentially dangerous glucose conditions, including hypoglycaemia, rapid glucose changes and dehydration.
Continuous multi-day operation presents further challenges. The hydrogel must continue collecting sweat, the sensor surfaces must resist biological contamination and disposable components must be easy to replace. Future models would also need to account more precisely for the delay between changes in blood and changes measured in sweat.
The prototype does not currently combine chemical sensing with the heart rate, oxygen, temperature and movement measurements found in existing smart rings. The research team plans to explore hybrid rings that unite biochemical and biophysical monitoring in one device.
It Should Not Replace an Approved Glucose Monitor
CHARM’s results are encouraging, but the ring should not be confused with a commercially approved continuous glucose monitor. It remains an experimental research platform and is not available as a consumer medical device.
The US Food and Drug Administration has warned consumers against using smartwatches or smart rings that claim to measure blood glucose independently without piercing the skin. The agency’s smart ring glucose safety communication states that it has not authorised, cleared or approved a watch or ring that performs this function on its own.
Inaccurate glucose readings can lead to incorrect insulin or medication decisions, potentially causing dangerously low blood sugar. Until a biochemical ring completes extensive clinical validation and receives appropriate regulatory authorisation, treatment decisions should continue to rely on approved blood glucose meters or continuous glucose monitors.
A Possible New Direction for Wearable Health Technology
CHARM represents a different vision for smart rings. Instead of only measuring pulse, motion and temperature, future wearables could continuously observe the chemical processes associated with food, exercise, medication and disease.
That capability could give researchers and healthcare professionals a more detailed view of how metabolic changes unfold throughout an ordinary day. Monitoring several biomarkers together may also prove more informative than treating glucose, ketones, lactate or nutrition as isolated measurements.
The prototype is still too early for medical or consumer use. Its small-scale testing, personalised calibration, limited water resistance and 12-hour operating time all require improvement.
Even so, fitting passive sweat extraction, four simultaneous chemical sensors, wireless electronics and a flexible battery into a ring is a significant engineering achievement. It suggests that future smart rings may do more than calculate sleep or activity scores. They may eventually provide a continuously updated biochemical picture of the body from nothing more than the sweat produced beneath a finger.
