Wearable Sensor Technology: A Builder's Guide to Choosing the Right Sensors

"A wearable is only as good as the signal it captures. "

The enclosure, the app and the cloud all sit downstream of one decision: which sensor technology goes against the skin. Getting that right and everything above has clean data to work with; getting it wrong and no amount of software rescues a noisy signal.

This raises a practical question:
Which wearable sensor technology fits your product and what does that choice lock in for accuracy, power and regulatory effort?

This guide walks wearable sensor technology from a builder's point of view. We cover the core sensor types and what each one measures, the biochemical sensors changing the field, the trade-offs that decide which sensor fits, plus what the choice means once the device has to clear EU MDR.

For the layered system around the sensor, our companion piece on the sensor stack architecture covers the rest.

Table of Content

What Wearable Sensor Technology Covers

Wearable sensor technology is the set of on-body sensors that turn a physical or chemical signal from the body into wearable data, the engine behind continuous health monitoring and preventive medicine.

Across the wider field of wearable technology, these on-body sensors collect data continuously and stream it to mobile devices, spanning biophysical sensors that read movement and optical or electrical signals plus biochemical sensors that read markers in sweat or interstitial fluid. Everything the product later does depends on the quality of that first reading.

How Wearable Sensors Read Biophysical vs Biochemical Signals

Biophysical sensors dominate today's wearables. They measure heart rate, motion, temperature, physical activity and electrical activity, so they cover most vital signs and stress levels. For example, an optical sensor at the wrist reads pulse, while an accelerometer reads steps and sleep.

Biochemical sensors are the newer frontier. They measure analytes such as glucose or lactate, which opens continuous readings that a watch cannot reach. However, they bring harder problems around calibration and skin contact.

Why the Sensor Choice Leads for Consumer Wearables

The sensor sits at the bottom of the stack, so its limits are upwards relevant. A weak signal forces heavier filtering, which costs power and adds latency. So the sensor decision constrains battery life, form factor and even the clinical claim you can make.

Therefore the sensor is a product decision and not a component pick made late.

From consumer wearables to health care devices, teams that choose it early design the enclosure, the placement and the power budget around it. It also sets whether the device supports early detection of chronic diseases such as heart disease that medical professionals can act on.

-> In short: Wearable sensor technology splits into biophysical and biochemical sensors. The sensor is lowest in the stack, so its limits shape everything above it. Choose it first.

The Core Sensor Types

Most wearables combine a handful of proven wearable sensing technologies. Knowing what each one measures, plus where it struggles, is the heart of the selection.

Optical Sensors (PPG) and SpO2

Photoplethysmography, or PPG, shines light into the skin and reads the reflection to track blood volume. It gives heart rate, heart rate variability and, with more wavelengths, blood oxygen saturation.

For instance, most wrist and ring wearables run on PPG because it is small and low power.

Their weakness is signal quality. Motion, cold skin and darker skin tones all change the reflected light, so a robust PPG design needs careful optics and motion compensation.

Biopotential (ECG, EEG, EOG, EMG)

Biopotential sensors read the body's own electrical activity through skin electrodes.

An ECG reads the heart,
an EEG reads brain activity,
an EOG reads eye movement
and an EMG the muscles.

A single-lead ECG on a watch or chest patch is now common for rhythm detection.

Electrodes need good skin contact, so dry electrodes trade a little signal quality for comfort. So placement matters more here than with any other sensor.

Motion, Temperature and Pressure Sensors

An accelerometer, usually part of an inertial measurement unit, reads movement and orientation.

It drives step counts, sleep staging and fall detection and it is the sensor teams use to measure physical activity.
It is cheap, tiny and sips power, so it appears in almost every device.
Skin temperature sensors add context, tracking temperature variations such as fever trends or menstrual-cycle signals.
Pressure sensors and vibration sensors extend the set for gait and respiration.
On their own they are simple, yet combined with PPG and motion they sharpen the whole picture.

-> In short: The core set is optical (PPG, SpO2), biopotential (ECG and related), plus motion and temperature. Each has a clear strength and a clear failure mode. Most products fuse several.

What To Do:

Map each metric your product claims to the sensor type that measures it and don't assume one sensor covers all.
For any optical design, test signal quality across skin tones, motion and cold conditions early.
Treat electrode placement and skin contact for biopotential sensors as a design input.

Biochemical and Next-Generation Sensors

The fastest-moving part of wearable sensor technology reads chemistry. These wearable biosensors, a class of chemical sensors, promise data no optical or motion sensor can reach, though they raise the engineering and regulatory bar.

Chemical Sensors: Continuous Glucose and Analyte Sensing

Continuous glucose monitors work by measuring glucose in interstitial fluid through a tiny under-skin filament.

They have moved from niche to mainstream by enabling continuous real time monitoring, so they are the clearest proof that biochemical wearables can scale. Similar approaches track:

glucose levels
lactate
ketones
uric acid
drug levels

The hard parts are calibration drift and the skin interface. As a result, these devices carry heavier validation and a higher medical-device class than a step counter.

Sweat, Microneedle and Environmental Sensors

Sweat sensors, galvanic skin response sensors and microneedle patches read biomarkers at the skin surface or just beneath it. They open therapeutic drug monitoring and hydration tracking from a small patch. Meanwhile, environmental sensors add UV exposure or air-quality context.

Most of these are still maturing, but still point to where the field is heading, so a build partner should track them even when today's product uses only biophysical sensors.

-> In short: Biochemical sensors, led by continuous glucose monitoring, read markers physics-based sensors cannot. They deliver richer data at the cost of harder calibration and a higher regulatory class.

Choosing the Right Sensor: The Trade-offs

No sensor is best in the abstract. The right wearable sensor technology falls out of four trade-offs weighed against the product's intended use.

Accuracy and Signal Quality

Accuracy is the first filter, so it depends on context:

A PPG heart rate that is fine at rest can drift during exercise, so the claim has to match the conditions of use. For a regulated device, the accuracy you state becomes a promise you must validate.

Signal quality also decides how much processing sits downstream. A cleaner raw signal means fewer noisy data points for the algorithm to clean, so it means lighter algorithms, which saves both power and development time.

Power, Placement and Form Factor

Power draw is second:

An accelerometer is almost free and cost effective, while continuous optical sampling or a biochemical sensor can dominate the energy budget. Therefore the sensor choice sets the battery and power source, which sets the size and the charging rhythm.

Placement decides what is even measurable:

The wrist suits motion and PPG, the chest suits ECG, the upper arm suits glucose. In contrast, forcing a sensor onto the wrong site for form-factor reasons usually wrecks the signal.

-> In short: Weigh accuracy, signal quality, power and placement against the intended use. The best sensor is the one whose limits your product can live with, on the body site the signal genuinely needs.

Sensor Technology and EU MDR

For a medical wearable, the sensor choice is a regulatory decision as much as a technical one. Under EU MDR, any accuracy or clinical claim you make about a sensor is part of the intended purpose, so it has to be proven.

Accuracy Is a Claim You Must Prove

The moment a wearable states a measurement, that number becomes a claim under MDR.

You need verification that the sensor measures what it says, plus validation that the measurement is clinically meaningful. Peer-reviewed work such as this review of wearable sensors for health monitoring shows how wide real-world accuracy can vary.

So a modest, well-evidenced claim beats an ambitious one you cannot defend. The sensor and its validation evidence travel together into the technical file.

Risk, Software and Class

Sensor risk feeds the risk-management file under ISO 14971.

A missed arrhythmia or a wrong glucose reading is a patient-safety hazard, so the analysis has to be thorough. The higher the stakes of the reading, the higher the device class.

The processing on top of the sensor is usually software as a medical device, so it follows the IEC 62304 lifecycle. The sensor and its algorithm are assessed as one system.

-> In short: Under MDR, a stated measurement is a claim you must verify and validate. Sensor risk drives ISO 14971 and the device class, while the algorithm on top follows IEC 62304.

What To Do:

Write the measurement claim and its conditions of use before choosing the sensor, because the claim sets the validation burden.
Start the ISO 14971 risk file with the sensor's failure modes and not at the end of development.
Treat the sensor and its processing algorithm as one regulated system from day one.

Building a Wearable Around the Sensor

The sensor decision is cheapest to get right at the concept stage. Once the enclosure, board and claims are set, changing the sensor means redoing most of them.

Decide the Sensor in the Concept Phase

Pick the sensor technology alongside the intended use, before the industrial design locks.

That way the placement, the power budget and the accuracy target all reinforce each other. As a result, the build runs on a signal the rest of the system can trust.

This is also where an experienced partner earns its place. The trade-offs are well understood, so the value is in weighing them against your specific product early.

Sensor Fusion, Machine Learning and Health Monitoring

Few products rely on one sensor, so most serious wearables fuse PPG, motion and temperature into a reading none delivers alone. Machine learning then turns the fused signal into the metric a clinician acts on, the basis of wearable health monitoring for real health conditions, well beyond step counts.

For teams building this, our wearables and custom hardware work starts from the sensor and designs outward. The sensor leads, so the product follows.

-> In short: Choose the sensor in the concept phase, alongside the intended use, then design the device around it. Most products fuse several sensors, so plan the combination early.

What To Do:

Lock the sensor technology at concept, before industrial design and the board layout.
Plan sensor fusion up front when one signal cannot carry the claim on its own.
Budget power, placement and validation around the sensor from the first sprint.

Closing Thoughts

Wearable sensor technology is the decision the whole product works on. The sensor sets the signal, the signal sets the claim, then the claim sets the regulatory path. Choose it in the concept phase and the rest of the build reinforces it.

When your team is scoping a wearable, fixing the sensor technology, its placement and its accuracy target early is the fastest way to a device that survives both the lab and the technical file. That is exactly the work we fold into custom wearable development, before the design locks.

FAQs on Wearable Sensor Technology

Q1: What sensors are used in wearable devices?

A1: Most wearables use a small set of sensor types. Optical PPG sensors read heart rate and blood oxygen, biopotential electrodes read ECG, accelerometers read motion and sleep, plus temperature sensors add context. Biochemical sensors, led by continuous glucose monitors, read markers in fluid under the skin. Most products fuse several of these into one stream of health data rather than relying on one sensor.

Q2: What is the difference between PPG and ECG in a wearable?

A2: PPG uses light to estimate heart rate from blood-volume changes, so it is small, low power and easy to place at the wrist. ECG reads the heart's electrical signal directly through electrodes, so it is more accurate for rhythm and can flag arrhythmia, but it needs good skin contact and careful placement. Many devices use PPG for continuous tracking and add a single-lead ECG for on-demand checks.

Q3: How accurate is wearable sensor technology?

A3: Accuracy depends on the sensor, the body site and the conditions. A PPG heart rate is reliable at rest but drifts during motion, while a medical-grade continuous glucose monitor holds tighter tolerances. For a regulated device the stated accuracy becomes a claim that must be verified and validated, so the honest figure matters more than the best-case one.

Q4: Does wearable sensor technology fall under EU MDR?

A4: It depends on the intended purpose. A wearable making a medical claim about a measurement is a medical device under EU MDR, so its sensor accuracy needs verification and validation, its risks need an ISO 14971 file, plus its software follows IEC 62304. A pure fitness or wellness device with no medical claim usually sits outside MDR, though the claim and not the hardware, is what decides.