Wearable Health Tech

What Is a Continuous Glucose Monitor — and Who's Actually Using One?

A continuous glucose monitor, or CGM, is a small sensor worn on the skin — usually the back of the upper arm — that measures glucose (blood sugar) levels throughout the day and night. It does this by reading interstitial fluid, the liquid between your cells, rather than blood directly.

Historically, CGMs were prescribed for people managing type 1 or type 2 diabetes. Today, they're being marketed aggressively to people without diabetes — athletes optimising performance, biohackers tracking diet response, and people who are simply curious about how food affects their energy levels.

In clinical practice, this is often missed because patients assume a "normal" fasting glucose means their blood sugar is stable all day. It frequently isn't. A CGM can reveal significant spikes after meals that a standard HbA1c test — which measures average blood sugar over three months — would never catch.

The market leaders include Abbott's FreeStyle Libre and Dexcom G7. Newer entrants are designing sleeker, prescription-free versions specifically for wellness use. If you're in India and considering whether a CGM is right for your health situation, speaking with a general physician first is strongly advisable — especially if you have a family history of diabetes or metabolic conditions.

What Do Smart Rings Actually Measure?

The Oura Ring — currently the dominant player in this category — sits on your finger and continuously reads heart rate, skin temperature, blood oxygen saturation (SpO2), and movement. From these signals, it generates metrics like sleep stages, readiness scores, and respiratory rate.

The Oura and its competitors (Samsung Galaxy Ring, Ultrahuman Ring Air) are genuinely impressive pieces of engineering. But the word "measure" deserves scrutiny here. These rings don't directly measure your stress or recovery — they infer it from physiological signals using proprietary algorithms. That's not a flaw, it's just how the technology works, and knowing the difference matters.

What the research does support: heart rate variability (HRV) — the tiny fluctuations in time between heartbeats — is a legitimate marker of nervous system health and recovery. A consistently low HRV can be a signal worth discussing with a cardiologist or general physician, especially if accompanied by symptoms.

What the research is less clear on: whether acting on daily readiness scores from a ring actually improves long-term health outcomes. The long-term studies simply haven't caught up with the technology yet.

The Accuracy Question Nobody Wants to Talk About

Both CGMs and smart rings are remarkably accurate for consumer devices. But "consumer accurate" and "clinically accurate" are not the same thing.

CGMs approved for diabetes management are validated against blood glucose meters. When used off-label for wellness, that calibration doesn't necessarily hold the same way. A CGM might show a glucose spike after coffee that looks alarming but falls within a perfectly normal physiological range — triggering unnecessary anxiety or, worse, unnecessary dietary restriction.

Smart rings fare similarly. Independent studies on the Oura Ring have shown solid accuracy for resting heart rate and body temperature detection. Sleep staging accuracy — the ring telling you how much deep sleep versus REM sleep you got — is more variable. It's better than nothing, but it shouldn't be used to make clinical decisions about a sleep disorder. If you suspect you have one, see a pulmonologist who can arrange a proper sleep study.

Who Benefits Most From These Devices?

This isn't a technology for everyone, and the honest answer is that the people who tend to benefit most are those who already have context to interpret the data.

People managing or at risk of diabetes get the clearest value from CGMs. If you or a family member has been told you have prediabetes — a state where blood sugar is higher than normal but not yet in the diabetic range — a CGM worn for two to four weeks can be a genuinely eye-opening way to understand which foods and habits are driving the problem. An endocrinologist near you can help you interpret the results properly.

Athletes and people in structured training get real, actionable data from smart ring HRV tracking. Many coaches now use HRV trends — not single readings — to decide when athletes should push hard and when they should rest.

People with chronic conditions — such as thyroid disorders, PCOS, hypertension, or chronic fatigue — may find that continuous data reveals patterns their quarterly blood tests don't. That said, this data should be shared with a qualified doctor, not acted on alone.

The Risks of Self-Monitoring Without Guidance

Wearable health tech can be empowering. It can also fuel anxiety, orthorexia (an obsessive focus on "healthy" eating), or a false sense of security.

Someone wearing a CGM who sees a glucose spike after a banana may cut out fruit entirely — which isn't necessarily the right response. Someone whose smart ring reports poor sleep for a week might catastrophise about their health when the real cause is simply a busy period at work.

The risk isn't the device; it's the lack of medical context around the data. A dietitian can help you interpret glucose responses in relation to your whole diet. A physiotherapist can help contextualise recovery data in relation to your training load. These devices work best as conversation-starters with professionals, not as standalone decision-makers.

If you've been tracking data that's genuinely worrying you — unusual glucose patterns, persistently poor sleep scores, low oxygen readings — book an appointment with a doctor rather than trying to diagnose the problem yourself through forum posts.

What to Look for Before You Buy

A few practical points, because the marketing in this space is loud:

For CGMs: In India, most CGMs still require a prescription for diabetes-related use. Abbott FreeStyle Libre sensors are available through many diagnostic centres and pharmacies. If you're buying one for wellness use, clarify this with your pharmacist or doctor.

For smart rings: Ensure the device has regulatory approval (CE mark, FDA clearance) for any specific health claims. A ring that claims to detect atrial fibrillation (an irregular heart rhythm) should have validated that claim in proper clinical studies — most currently don't, or haven't published that data transparently.

Sensor wear duration matters: Most CGM sensors last 10 to 14 days. Running one or two "experiments" — once before and once after changing a dietary habit — gives far more actionable data than continuous wear, which can generate noise.

For children and older adults, don't make decisions about wearable monitoring without consulting a paediatric doctor or appropriate specialist first.

The Bigger Picture

Wearable health tech is not a replacement for healthcare. No CGM will catch a thyroid nodule. No smart ring will diagnose a heart valve problem. What these devices do is provide a layer of continuous, accessible data that didn't previously exist for most people.

Used thoughtfully — with medical guidance, realistic expectations, and a willingness to bring the data to a professional — they genuinely can close gaps in how we monitor health between clinic visits. That's a meaningful step forward.

But the real value of these tools may ultimately be less about the data themselves and more about the conversations they start. A patient walking into a doctor's appointment in Kolkata with two weeks of CGM data in hand is having a very different and richer conversation than one who comes in saying, "I just feel off."