Wearable Sensors: Types, Power and Placement

Concept render

Wearable sensors fall into four groups: motion (IMU, barometer), body signals through the skin (PPG, ECG, skin temperature, EDA, bioimpedance), sound (microphones) and surroundings (ambient light, GNSS). Each has its own power draw and placement needs, and the claims you make about the outputs decide whether the product stays general wellness.

Wearable sensors decide what a ring, band or pendant can report, how long its battery lasts and where it must touch the body. This guide maps the common types of wearable sensors, gives a real part example for each with power figures from the vendor's own datasheet, compares ring, wrist and chest placement, and explains where FDA draws the line on health claims. It links to deeper guides for each sensor instead of repeating them.

This is an engineering summary. Part numbers are examples that show typical figures. None of them is a recommendation, and vendors revise datasheets. All sources were read on November 12, 2026.

What types of wearable sensors are there?

The table lists ten sensor types found in wearables. Each row names one example part and quotes a power figure from that part's own document, as of November 2026. Conditions differ from row to row, so use the figures to see the scale, then measure in your own design.

The spread is wide. A barometer sampling once a second draws a few microamps, while GNSS in continuous tracking draws milliwatts. The sensors that run all the time set the battery size.

Which wearable health sensors work through the skin?

These sensors need steady skin contact, so the housing design matters as much as the chip.

PPG for pulse

A PPG sensor sends LED light into the skin and measures what returns. Firmware estimates pulse rate from the rhythm in that signal. TI's AFE4950 is built for this: it drives up to 8 LEDs, reads up to 4 photodiodes per phase, and lists optical heart-rate monitoring for wearables and hearables among its applications (TI AFE4950 datasheet, as of November 2026). Motion is the main source of error. Our guide to PPG motion artifacts and accelerometer testing shows how to test it.

ECG for the heart's electrical signal

An ECG sensor uses electrodes and a biopotential front end. On a watch, one electrode sits on the case back and the user touches a second one with the other hand. FDA lists electrocardiogram recording and analysis devices as examples of products that are not general wellness products (FDA guidance, as of November 2026). Our ECG wearables guide covers the front end, noise and the FDA line in detail.

Skin temperature

A digital temperature sensor placed against the skin reads the contact point, which changes with blood flow, air and fit. TI's TMP117 has a maximum error of ±0.1 °C from -20 °C to 50 °C and draws 3.5 µA at a 1 Hz conversion cycle. TI lists wearable fitness and activity monitors among its applications (TI TMP117 datasheet, as of November 2026). The sensor is accurate. The thermal path from skin to sensor usually limits the reading. See skin temperature sensor design: ring vs wrist.

EDA and bioimpedance

Electrodermal activity (EDA), also called galvanic skin response, is the change in skin conductance as sweat glands respond to the nervous system. TI's application brief describes measuring it between two electrodes touched by fingers of the same hand on a wrist-worn device, usually with a low-frequency AC excitation in the tens of hertz. It names high contact impedance from small electrodes and the need for low power as the key challenges (TI SBAA556, as of November 2026).

Bioimpedance uses electrodes in a similar way to measure the impedance of tissue. TI's EDA brief lists the AFE4500 as also supporting bio-impedance (Bio-Z) (TI SBAA556, as of November 2026). The AFE4950 is different: TI lists continuous low-power impedance monitoring between two electrodes, reusing the ECG chain, and does not call it bioimpedance (TI AFE4950 datasheet, as of November 2026). In a wellness product, these signals support features such as stress or recovery trends. They should not be presented as a measure of any condition.

Which sensors track motion, altitude and sound?

IMU

Almost every wearable has an accelerometer, and many add a gyroscope. The Bosch BMI270 combines both in a 2.5 × 3.0 mm package, 0.83 mm high. Its accelerometer alone runs down to 4 µA in low power mode, while the full IMU in normal mode draws 685 µA (Bosch BMI270 datasheet, as of November 2026). That gap is why firmware keeps the gyroscope off until it is needed. Our guide to types of motion sensors in wearables covers accelerometers, gyroscopes and magnetometers in depth.

Barometer

A pressure sensor detects small altitude changes, such as climbing stairs. Bosch lists the BMP390 at a typical relative accuracy of ±3 Pa, equal to ±0.25 m, with 3.2 µA at 1 Hz and a 2.0 × 2.0 × 0.75 mm package (Bosch BMP390 datasheet, as of November 2026). The housing needs a vent that lets air in and keeps water out.

Microphone

Voice wearables use MEMS microphones. TDK lists the T5838 as a bottom-port PDM microphone with 68 dB SNR, 133 dB AOP and an Acoustic Activity Detect mode that draws as little as 20 µA (TDK InvenSense T5838, as of November 2026). The microphone needs an acoustic port in the housing. See PDM vs I2S vs analog MEMS microphones for interface choices.

Which sensors read light and location?

An ambient light sensor sets screen brightness or logs daylight exposure. TI's OPT3001 measures from 0.01 lux to 83k lux, draws 1.8 µA typical and comes in a 2.0 × 2.0 × 0.65 mm package. TI notes its infrared rejection helps when the sensor sits under dark glass (TI OPT3001 datasheet, as of November 2026). UV sensors work in a similar way with a filter for ultraviolet light. Check the specific vendor datasheet for their figures.

GNSS gives position outdoors, and it is the largest power user in this list. The u-blox MIA-M10Q receives GPS, GLONASS, Galileo and BeiDou at the same time and lists 25 mW in continuous tracking mode. u-blox describes it as suited to compact wearable and tracking designs (u-blox MIA-M10Q datasheet R08, as of November 2026). Most wearables run GNSS only during workouts or borrow position from the phone. The antenna also needs space, as our GNSS antenna placement guide explains.

How do smart ring sensors differ from wrist and chest placement?

Where the device sits limits which sensors work. The table is engineering reasoning about typical layouts. It does not describe any one product.

Smart ring sensors face the tightest space and battery limits. A ring holds its sensors close to the skin on the finger, which can help optical contact when the fit is right. It also has no room for extras, so each sensor has to earn its place.

How do sensor power figures add up?

Add the always-on floor first. As a worked example, take four parts from the table, each at the low-power setting quoted from its datasheet: the BMI270 accelerometer at 4 µA, the BMP390 at 3.2 µA, the TMP117 at 3.5 µA and the OPT3001 at 1.8 µA. Together they draw about 12.5 µA. That is our arithmetic on the cited figures, and it leaves out the microcontroller, the radio, PPG LED pulses and the regulator.

Then add the bursts: PPG readings, gyroscope sessions, GNSS fixes and radio syncs. These often dominate the total. Measure the real profile on a prototype rather than adding datasheet typicals. Our guide to testing battery life claims shows how.

Where is the line between wellness and medical claims?

Intended use and claims decide whether a product is a medical device. Choosing a sensor does not settle it. FDA's general wellness guidance, issued January 6, 2026, says FDA may consider products that use non-invasive sensing, such as optical sensing, to estimate parameters like blood pressure, oxygen saturation, blood glucose or heart rate variability to be general wellness products, when outputs are intended solely for wellness uses and the listed conditions are met (FDA guidance, as of November 2026).

The same guidance says products are not general wellness when they are intended to measure or report physiologic values for screening, diagnosis, monitoring, alerting or management of a disease or condition. It names electrocardiogram recording and analysis devices among its examples. It also lists items in labeling, ads or the interface that take a product out, such as references to specific diseases or diagnostic thresholds and claims of medical grade or clinical equivalence (FDA guidance, as of November 2026).

So the same PPG sensor can sit in a wellness band that shows pulse trends during exercise, or in a regulated product with different claims and review. Our article on the FDA general wellness guidance and wearable claims walks through the wording. Duobay builds general wellness products only. See health wearable development for that scope.

What should you decide before choosing wearable sensors?

Work through these with your hardware and product teams.

• Which outputs will the app show, and is each one inside the general wellness wording?
• Which sensor is always on, and which runs on a schedule or on demand?
• What is the sleep floor of each sensor at the sample rate the firmware will use?
• Which sensors need skin contact, and how does the housing hold them against the skin?
• Which sensors need a window or an opening in the housing: light, PPG, microphone port, barometer vent?
• How will accuracy be checked for each output, and on which group of people?
• Which sensors share an interrupt line or a bus, and can the MCU sleep while they collect data?

If you are planning a wellness ring, band or pendant and want the sensor set chosen with the battery and housing, tell us about your device.

Sources. All pages accessed November 12, 2026. Re-read the current datasheet revision for each part before you rely on any figure.

• FDA, General Wellness: Policy for Low Risk Devices, issued January 6, 2026 (link)
• Bosch Sensortec, BMI270 datasheet (link)
• Bosch Sensortec, BMP390 datasheet (link)
• Texas Instruments, TMP117 datasheet, SNOSD82D, revised September 2022 (link)
• Texas Instruments, AFE4950 datasheet, SBASA37B, revised July 2021 (link)
• Texas Instruments, Electrodermal Activity (EDA) for Wearable Devices, SBAA556, September 2022 (link)
• Texas Instruments, OPT3001 datasheet, SBOS681C, revised November 2017 (link)
• TDK InvenSense, T5838 product page (link)
• u-blox, MIA-M10Q data sheet, UBX-22015849 R08, January 30, 2026 (link)