Wearables
Wearable Device Development
Raonebytes develops wearable device prototypes for health, sports, safety, industrial and consumer use cases: fitness and activity bands, smart watches, hearables and body-worn trackers. We take on the parts that decide whether a wearable works on a person rather than on a bench, which is power, sensing under motion, radio performance next to tissue and a housing that survives daily wear.
The short answer
Wearable device development covers the miniaturised electronics, biosensing front end, Bluetooth Low Energy firmware, battery and charging system and skin-contact enclosure needed to put a working device on a wrist, ear or torso. A mid-complexity wearable prototype typically costs $8,000 to $20,000 and takes 8 to 14 weeks, with most of the engineering going into power budgeting, sensor signal quality under motion and the mechanical fight for volume rather than the companion app.
Common builds
Fitness and activity bands
Continuous heart-rate and SpO2 monitoring
Hearables and ear-worn sensors
Body-worn safety and lone-worker trackers
Sleep, recovery and skin-temperature tracking
What Raonebytes delivers
Miniaturised electronics
Compact and rigid-flex PCB design where the antenna keepout, sensor optics, battery footprint and charge contacts are placed together rather than in sequence. Stack-up, component height and assembly process are chosen against the enclosure section, not after it.
Low-power firmware
BLE GATT services, sensor sampling schedules, on-device buffering, logging and secure over-the-air update, written around a measured sleep-current budget. Wake sources, connection intervals and radio duty cycle are treated as the primary power controls because they are.
Power and charging system
LiPo or coin-cell sizing against a real duty cycle, protection and charge circuitry, fuel gauging, and a charging interface (pogo pins, magnetic contacts or inductive) chosen for corrosion and sweat exposure. Battery life is verified by instrumented measurement rather than datasheet arithmetic.
Wearable mechanical and validation
Ergonomic housings, straps, optical windows, sealing strategy and charging docks, with printed and machined iterations worn during testing. Validation covers on-body radio range, battery life, sensor performance during movement and ingress checks against the target rating.
What makes this hard
The constraints that decide whether a design survives contact with the real world.
Average current, not peak current, sets battery life
A wearable spends almost all of its time asleep, so a few microamps of unintended leakage from a floating pin, an always-on regulator or a sensor left in continuous mode can halve runtime while the active-mode figures look perfect. The only reliable method is measuring the full current profile across a real duty cycle, including advertising, connection events and sensor bursts.
Motion artifacts in biosensing
PPG heart-rate measurement depends on tiny changes in reflected light, and movement of the sensor against the skin produces artifacts far larger than the signal being measured. Usable data comes from mechanical work (contact pressure, optical isolation between LED and photodiode, ambient light rejection) combined with accelerometer-aided filtering, and no amount of downstream algorithm rescues a bad optical assembly.
The human body detunes the antenna
Tissue is electrically lossy and high in permittivity, so an antenna tuned on a bench shifts frequency and loses efficiency the moment the device is worn. Matching has to be tuned with the device in its enclosure on a body or phantom, and the loss of link budget needs to be accounted for before the mechanical design is frozen.
Volume, heat and the skin interface
Battery capacity, antenna clearance, sensor optics and component height all compete for the same few cubic centimetres, and every gain in one is a loss somewhere else. Heat has nowhere to go except into the wearer, so charging currents and processing loads are constrained by touch-temperature limits (safety standards commonly treat sustained skin contact above roughly 43 C as the ceiling) rather than by silicon ratings.
Standards and protocols that shape the design
Identifying these early is what keeps them from forcing a redesign later.
- Bluetooth Low Energy and the GATT model
- BLE exposes data as a hierarchy of services and characteristics over GATT, with adopted profiles such as Heart Rate, Battery and Device Information available as 16-bit UUIDs and anything proprietary carried on 128-bit custom UUIDs. Using adopted services where they fit gives you interoperability with existing phone apps and health platforms, while connection interval and latency negotiation is where most of the power behaviour is decided.
- ISO 10993 biocompatibility
- Any material in prolonged contact with skin falls under the ISO 10993 series, which requires biological evaluation within a risk-management process: cytotoxicity (part 5), skin sensitisation (part 10) and irritation (part 23) are the parts most often relevant to a wearable. Testing is carried out by specialist laboratories on the finished device with its actual finishing process, so the practical design lever is selecting known biocompatible grades for straps, adhesives, coatings and optical windows early.
- FCC Part 15 and CE Radio Equipment Directive
- A 2.4 GHz BLE product is certified in the US under FCC Part 15 Subpart C (with unintentional-radiator requirements under Subpart B) and marketed in Europe under the Radio Equipment Directive using harmonised standards such as EN 300 328 for the radio and the EN 301 489 series for EMC. Certification is issued on the basis of testing at an accredited laboratory: Raonebytes designs for pre-compliance, arranges and supports the test campaign and handles the fixes, and using a pre-certified radio module within its granted conditions substantially reduces the radio test scope.
- RF exposure and SAR
- Regulators require an RF exposure assessment, but low-power BLE wearables usually fall below the thresholds that trigger full SAR measurement, so the obligation is a documented justification rather than a test campaign. Devices that add a cellular radio or run at materially higher output power lose that exclusion and need laboratory SAR testing at the intended wear distance.
- IEC 60529 ingress protection
- IPX4 covers splashing, IPX7 covers immersion to one metre for thirty minutes, and IPX8 covers conditions agreed with the manufacturer beyond that. These tests use fresh water under defined conditions and do not represent warm pressurised shower water, soap or sweat, so a device claiming sweat and shower resistance needs corrosion-aware material and finish choices plus its own soak and salt exposure tests on top of the rated figure.
Typical technology stack
Compute
Ultra-low-power wireless SoCs such as the Nordic nRF52 and nRF53 families or comparable BLE parts, selected on retained-RAM sleep current, peripheral autonomy and radio efficiency rather than headline clock speed. The ability to run sensor collection through DMA and low-power peripherals while the core stays asleep matters more than raw processing throughput.
Biosensing front ends
Integrated PPG modules with green emitters for wrist heart rate and red plus infrared for SpO2, analog front ends with high common-mode rejection for single-lead ECG, and thermistors or digital sensors with a deliberate thermal path for skin temperature. Each of these lives or dies on the mechanical detail around it: window material, contact pressure, optical isolation and electrode placement.
Motion sensing
Low-power MEMS accelerometers and six-axis IMUs for step counting, gesture and activity classification, sleep staging and wear detection. Their hardware interrupts (wake-on-motion, activity and tap detection) also act as the system power gate, letting the device stay in deep sleep until motion is worth processing.
Power
Small LiPo cells with CC/CV charging, protection and temperature-qualified charge windows for higher-capacity designs, or coin cells such as CR2032 where the average current is tiny, in which case high internal resistance forces bulk capacitance to support radio transmit peaks. Fuel gauging is either coulomb counting or model-based voltage estimation, chosen against how much error the product can tolerate in its battery indicator.
Interconnect and mechanics
Rigid-flex and HDI construction to fold electronics into a curved section and remove fragile board-to-board connectors, with component height budgeted against the enclosure cross-section. Optical windows, gaskets, adhesives and overmoulded straps are specified alongside the layout because they define both the sealing strategy and the skin-contact material set.
Connectivity and apps
BLE to a phone as the primary link, with optional Wi-Fi or LTE-M in the dock or companion device where data has to reach the cloud without a handset. On the software side that means a mobile bridge, secure pairing and bonding, time-synchronised logging and an over-the-air update path that can survive a failed transfer.
Why this matters
Wearables are unusually unforgiving because every requirement pulls against the others. More battery means less room for optics, a bigger antenna means less metal in the housing, more sensor sampling means shorter runtime, and a better seal means a harder charging interface. Getting those trade-offs wrong is not something a firmware revision fixes, because the decisions are locked into the board outline, the enclosure section and the battery footprint. Raonebytes designs the electronics, firmware, power system and mechanical housing as one problem, so the conflicts surface during the prototype instead of after tooling. Our compact consumer and robotics work, including the AI-based kids toy with its battery-powered enclosure, custom electronics and over-the-air update path, involved the same combination of small-format hardware, low-power firmware and manufacturable housing design.
Frequently asked questions
What does a wearable prototype cost?
A mid-complexity wearable with custom electronics, BLE firmware, a rechargeable battery and a bespoke enclosure typically runs $8,000 to $20,000 for a working prototype. Simpler enclosed devices start from $5,000. The main cost drivers are how many biosensing channels the device carries, how tight the volume target is and whether the housing needs sealing for immersion.
How long does a wearable build take?
Most wearable prototypes take 8 to 14 weeks from kickoff to a tested unit. Schematic and compact layout usually take 3 to 4 weeks, fabrication and assembly 2 to 3 weeks, and firmware plus integration the remainder. Mechanical iteration on the enclosure and optical assembly is the most common source of extra time, because those parts are usually revised after the first on-body tests.
How do you get realistic battery life out of a wearable?
By treating average current as the design target from day one: choosing an MCU on its sleep current, keeping the radio duty cycle and connection interval as long as the use case tolerates, and letting sensor interrupts wake the system instead of polling. We then measure the actual current profile over a representative day rather than estimating it, which is where unintended leakage and misconfigured peripherals show up.
Will heart-rate readings be accurate during exercise?
Optical heart rate is reliable at rest and degrades under motion, because movement of the sensor against the skin generates artifacts larger than the pulsatile signal itself. Consistent contact pressure, good optical isolation between emitter and photodiode, ambient light rejection and accelerometer-aided filtering are what close most of that gap. We set accuracy expectations against defined activity conditions rather than as a single headline number.
Does my wearable become a regulated medical device?
It depends on the claims you make, not on the sensors you fit. A device presented as general fitness or wellness is usually outside medical device regulation, while claims about diagnosing, monitoring or treating a condition can bring it under FDA oversight in the US and the EU Medical Device Regulation in Europe, which is a materially heavier route. This is worth settling before design freeze, and our medical device prototyping page covers what changes when you cross that line.
Do you handle FCC and CE certification?
Certification itself is issued on the basis of testing at an accredited test laboratory, so no design house can grant it. What we do is design for pre-compliance, run the radio and EMC risk down before submission, prepare the technical documentation, and support the lab campaign and any rework it triggers. Using a pre-certified BLE module within its granted conditions is often the fastest route, because it removes most of the intentional-radiator testing from your scope.
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