ECG Wearables: Sensors, Electrodes and the FDA Line

Concept render

ECG wearables measure the heart's electrical signal through skin electrodes and an analog front end, while most wellness bands estimate pulse optically with PPG. As of November 2026, FDA lists electrocardiogram recording and analysis devices as outside its general wellness policy, so an ECG rhythm feature is a regulated medical device function.

ECG wearables are watches, bands, rings and patches that record the heart's electrical activity. They look like fitness trackers, but the hardware and the rules differ. This guide explains how an ECG sensor differs from an optical heartbeat sensor, what the analog front end has to do, where noise comes from, and where FDA draws the line. Chip figures come from Texas Instruments datasheets. Regulatory text comes from fda.gov and the eCFR.

This is an engineering summary and not regulatory or legal advice. Datasheets and FDA documents change, so check the linked pages before you decide. All sources were read on November 12, 2026.

What is the difference between an ECG sensor and a heartbeat sensor?

Most "heartbeat sensors" in consumer wearables are optical. A PPG sensor shines LED light into the skin and measures how much comes back. The signal rises and falls with blood volume, so firmware can estimate pulse rate from it. An ECG sensor measures something else: the voltage the heart muscle produces as it contracts, picked up between electrodes on the skin.

The two need different hardware, and they sit on different sides of the FDA line. The table compares them. The rows on hardware and noise are engineering reasoning. The FDA row links to its source.

The FDA row comes from the general wellness guidance issued January 6, 2026 (FDA guidance, as of November 2026). For how PPG readings fail during movement, see PPG motion artifacts and how to test them. For the full sensor map of a wearable, see types of wearable sensors.

How does an ECG watch or band take a reading?

An ECG needs a closed electrical loop across the heart. A chest patch gets this from two electrodes a few centimeters apart on the torso. A watch or band has only the wrist, so it needs help from the other hand.

Two electrodes: the finger closes the loop

The common ECG watch layout puts one electrode on the back of the case, against the wrist, and a second on the crown, bezel or a side key. The user touches the second electrode with a finger of the other hand. The signal path then runs from one arm, across the chest, to the other arm. This gives a single-lead recording, and it only works while the finger is in place, so readings are on demand.

Three electrodes: a reference for the body

A third electrode lets the front end drive the body toward a known voltage. This is the right leg drive (RLD) idea, named after the clinical lead layout. TI's AFE4950 supports both 2- and 3-electrode configurations and has an RLD output to drive a third electrode (TI AFE4950 datasheet, as of November 2026). On a watch, the third electrode can share the case back with the first.

Patches and chest straps

A patch or strap sits on the chest, close to the heart, so it can record continuously with a larger signal. The tradeoffs are comfort, long-term skin contact and battery size.

What does the ECG analog front end need to do?

The ECG signal at the wrist is small and rides on large offsets and interference. A biopotential AFE amplifies the difference between electrodes, rejects what is common to both, digitizes the result and checks that the electrodes touch skin. The table compares two TI parts, using each datasheet's own figures as of November 2026. Conditions differ between the two documents, so do not compare the noise rows directly.

The two parts reflect two design choices. The ADS1292 is a dedicated two-channel ECG converter. TI lists both medical instrumentation and personal care and fitness monitors among its applications, and its data rate runs from 125 SPS to 8 kSPS (TI SBAS502C, as of November 2026). The AFE4950 combines a one-lead ECG chain with an optical PPG front end, so one chip can serve both sensors in a watch (TI AFE4950, as of November 2026).

Where does ECG noise come from on a wearable?

Three sources cause most of the trouble in a wrist or chest ECG: mains hum, electrode contact and motion.

Mains hum at 50 or 60 Hz

Power wiring couples into the body, and the body acts as an antenna. The interference shows up on both electrodes at once, so a good front end rejects it as a common-mode signal. TI's ADS1292 datasheet gives a CMRR of 120 dB typical and 105 dB minimum at 50 and 60 Hz (TI SBAS502C, as of November 2026). The same datasheet describes the RLD circuit as a way to counter common-mode interference from power lines and fluorescent lights. It senses the common mode of selected electrodes and drives the body with an inverted copy.

Board layout can throw that rejection away. The ADS1292 datasheet asks for the parasitic capacitance on each input filter to stay under 20 pF and to match. In its example, a 20 pF mismatch at a gain of 6 limits CMRR to 112 dB (TI SBAS502C, as of November 2026). Keep the two input paths symmetrical, short and away from switching regulators. Our PCB layout guide for small devices covers return paths and noisy power stages.

Electrode contact

In general, dry metal electrodes on a wearable make a higher and less stable contact than the gel electrodes used in clinics. That is engineering reasoning, not a TI statement. Skin moisture, hair and strap pressure all change it. TI notes that patient electrode impedances are known to decay over time and that connections need continuous monitoring (TI SBAS502C, as of November 2026). This is why lead-off detection matters. The AFE injects a small current and watches the response. If the electrode lifts off, the firmware can tell the user to adjust the device rather than record noise.

Motion

When the wrist or chest moves, the electrode shifts on the skin and the contact voltage changes. Muscle activity adds its own signal. A watch reading avoids most of this by asking the user to sit still. A patch that records all day needs firmware that flags noisy segments, helped by an accelerometer.

Which electrodes work on an ECG wearable?

The electrode is part of the housing, so the mechanical and electrical teams choose it together. Common choices for dry electrodes include stainless steel, gold or other plated metal on a molded part, and conductive coatings. The points below are engineering reasoning. None of them is a measured result.

• Area and shape. A larger contact area gives a more stable contact. A case-back electrode can be a ring or a pad shaped to the wrist.
• Material and finish. The material touches skin for hours. Choose a finish that resists sweat and wear, and check skin-contact data with the material supplier.
• Isolation. Each electrode must be isolated from the other and from any metal housing parts. The ECG inputs also need ESD protection that does not add leakage or mismatch.
• Antenna clearance. Metal electrodes near a Bluetooth antenna can detune it. Check the antenna in the real enclosure.

Where is the FDA line for ECG wearables?

General wellness guidance

FDA's general wellness guidance, issued January 6, 2026, says products are not general wellness products when they are intended to measure, estimate or report physiologic values for medical or clinical purposes, including screening, diagnosis, monitoring, alerting or management of a disease or condition. Its examples include "electrocardiogram recording and analysis devices" (FDA guidance, as of November 2026).

The same guidance lists labeling and interface items that take a product out of general wellness. They include references to specific diseases or diagnostic thresholds, alerts that recommend specific clinical action, and claims of clinical equivalence or medical grade (FDA guidance, as of November 2026). Our article on the FDA general wellness guidance and wearable claims walks through the full list.

Over-the-counter ECG software

The eCFR defines electrocardiograph software for over-the-counter use at 21 CFR 870.2345. The device "creates, analyzes, and displays electrocardiograph data" and "can provide information for identifying cardiac arrhythmias." The regulation adds that it "is not intended to provide a diagnosis." It is Class II with special controls, including clinical performance testing, software verification, human factors testing and labeling (eCFR 870.2345, as of November 2026).

FDA's De Novo database shows where that regulation came from. The "ECG App" from Apple Inc. received a De Novo decision on September 11, 2018, under regulation 870.2345, product code QDA (FDA De Novo DEN180044, as of November 2026). In practice, an ECG watch feature that flags atrial fibrillation is a regulated function, and the companies that ship one go through FDA review.

What this means for a wellness product

A general wellness product cannot add ECG recording or rhythm analysis and stay general wellness. It also should not describe a PPG pulse readout as an ECG. If your product needs to stay in the wellness category, use PPG for pulse and keep the claims to wellness uses. See health wearable development for how Duobay scopes those products.

Which standards come up when testing ECG devices?

Two names come up often. Both apply to ECG devices on the medical device side.

• IEC 60601-2-47. The particular standard for the basic safety and essential performance of ambulatory electrocardiographic systems. The current edition is 2.0, published February 16, 2012. The IEC page says it does not apply to systems that do not continuously record and analyze the ECG, such as intermittent event recorders (IEC webstore, as of November 2026).
• ANSI/AAMI EC13. Titled "Cardiac monitors, heart rate meters, and alarms." FDA's 1998 cardiac monitor guidance applies to most monitors covered by the EC13-1992 standard and recommends showing conformance to it (FDA cardiac monitor guidance, as of November 2026).

Which standards a product must meet depends on its classification and intended use. A regulatory specialist should make that list. For wellness heart-rate products, see heart rate accuracy testing with ANSI/CTA-2065 instead.

What should you decide before designing an ECG wearable?

Answer these before the schematic starts. The first one sets the rest.

• Is the product a general wellness device, or does it need an ECG feature that FDA regulates? Write the intended use before choosing parts.
• If heart rate is the goal, can PPG cover it, so the product needs no electrodes at all?
• How many electrodes will the housing allow, and where does the second hand or the chest touch them?
• Which electrode material and finish will touch skin, and has the skin-contact material been checked with its supplier?
• Which AFE is planned, and does its lead-off detection fit the electrode layout?
• How will you test mains hum rejection with the device on a person, not only on the bench?
• Which words will appear in the app, the box and the store listing, and has each one been checked against the FDA list?

If you are planning a general wellness wearable that tracks pulse with PPG, tell us about your device.

Sources. All pages accessed November 12, 2026. Re-read the current versions before you rely on any figure.

• FDA, General Wellness: Policy for Low Risk Devices, issued January 6, 2026 (link)
• eCFR, 21 CFR 870.2345 Electrocardiograph software for over-the-counter use (link)
• FDA De Novo database, DEN180044, ECG App (link)
• FDA, Cardiac Monitor Guidance (including Cardiotachometer and Rate Alarm), issued November 5, 1998 (link)
• Texas Instruments, ADS1291, ADS1292, ADS1292R datasheet, SBAS502C, revised April 2020 (link)
• Texas Instruments, AFE4950 datasheet, SBASA37B, revised July 2021 (link)
• IEC, IEC 60601-2-47:2012 webstore page (link)