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A FIELD GUIDE TO WEARABLE SYSTEMS

THE BODY
IS THE SPEC

Power, heat, sensing, radio, optics and trust, all forced into a thing someone has to wear.

ARYAN YADAV · 2026

01 · THE ACTUAL BRIEF

A PHONE GETS A DESK.
A WEARABLE GETS SKIN, SWEAT, HAIR, WEATHER, MOTION AND ATTENTION.

The enclosure is part of the computer. So is the body next to it.

An imagined flat lay of generic smart glasses, an earbud, a watch and a clip wearable on black fabric
ONE CATEGORY, FOUR BODY POSITIONSIMAGINED EDITORIAL IMAGE

A WEARABLE IS A LOOP

EVERY USEFUL MOMENT HAS TO MAKE THE ROUND TRIP.

Miss any step and the product becomes a sensor demo.

THE BODY HAS A VETO

IF IT IRRITATES THE SKIN, IT COMES OFF.

If it looks strange, it stays home.

If it dies at 5 p.m., the morning data does not matter.

The first product metric is still: did the person keep wearing it?

An imagined runner at dawn wearing a watch and a single earbud

THE LAB MOVES

THE SIGNAL HAS TO SURVIVE A REAL DAY.

Running, sleeves, traffic, sun, sweat, poor fit and a dying battery arrive together.

FIELD CONDITIONSIMAGINED EDITORIAL IMAGE

02

ENERGY

Battery capacity is the budget. Everything else is an argument about spending it.

ILLUSTRATIVE ARITHMETIC

1 Wh÷24 h=41.7 mW

That average has to cover sensing, memory, compute, radio, conversion loss and whatever the product does for the person.

A simple envelope, not a reference design.

THE ENERGY BUDGET

DESIGN THE IDLE STATE FIRST.

A rare expensive event can fit. A small permanent leak cannot.

Illustrative proportions. Real budgets depend on duty cycle, voltage rails, radio conditions and workload.

An imagined macro photograph of a small lithium pouch cell beside a caliper and a round wearable housing

CAPACITY HAS VOLUME

EVERY EXTRA HOUR HAS A SHAPE.

A thicker case, a larger watch, a tighter thermal path, a different charge ritual. Milliamp-hours eventually become industrial design.

BATTERY · ENCLOSURE · FITIMAGINED EDITORIAL IMAGE
An imagined open round wearable showing a copper wireless charging coil

CHARGING IS ARCHITECTURE

THE COIL ALSO WANTS THE CENTER.

It competes with the battery, antennas, sensors, magnets, shielding and the clean interior the designer drew first.

THE INSIDE IS ALREADY FULLIMAGINED EDITORIAL IMAGE

03

SENSING

A sensor does not collect reality. It collects a voltage shaped by placement, physics and noise.

An imagined macro view of two microphone ports behind textured black acoustic mesh

SOUND ENTERS THROUGH A HOLE

THE MODEL HEARS THE ACOUSTIC PATH FIRST.

Mesh, seal, wind, fabric, enclosure resonance and microphone spacing shape the input before software sees a sample.

MICROPHONE ARRAYIMAGINED EDITORIAL IMAGE

THE ACOUSTIC PATH

BETTER TRANSCRIPTS CAN BEGIN IN THE ENCLOSURE.

Software can suppress noise. It cannot recreate a signal the mechanical design never captured.

An imagined close view of a watch sensor touching skin with red optical light visible

CONTACT IS A VARIABLE

THE WRIST IS NOT AN OPTICAL BENCH.

Pressure changes. The watch slides. Skin and tissue scatter light. Motion can look like physiology.

OPTICAL SENSING ON SKINIMAGINED EDITORIAL IMAGE

A PPG READING IS CONDITIONAL

SIGNAL QUALITY IS PART OF THE MEASUREMENT.

Motion and poor skin contact can corrupt wrist PPG. See Pham et al., Scientific Reports, 2025.

An imagined thermal-style image of a wrist and watch with heat concentrated beneath the case

HEAT HAS NOWHERE TO GO

SKIN TURNS POWER INTO A PRODUCT FEELING.

The person never experiences watts. They experience a warm patch, a heavy frame or a battery warning.

POWER BECOMES TEMPERATUREIMAGINED EDITORIAL IMAGE

04

COMPUTE

The fastest operation is the one a cheap signal proves you do not need to run.

An imagined macro photograph of a dense generic wearable circuit board with sensors and a wireless chip

THE BOARD IS A NEGOTIATION

EVERY MILLIMETER HAS THREE OWNERS.

Routing, antennas, shielding, microphones, sensors, memory, power rails, flex cables and test points all need physical room.

GENERIC WEARABLE PCBIMAGINED EDITORIAL IMAGE

THREE SPEEDS OF THOUGHT

KEEP THE CHEAPEST LAYER AWAKE.

Representative modern MCUs now combine multiple CPU cores, radio, on-chip memory and edge ML support. Nordic's nRF54H20 is one example.

THE MEMORY WALL, MINIATURISED

MOVING DATA COSTS ENERGY TOO.

This is why model size alone is a weak proxy for wearable efficiency. Access pattern, precision, reuse and memory placement matter.

EVENT-DRIVEN COMPUTE

MAKE EXPENSIVE WORK EARN ITS WAKE-UP.

A sensor hub can stay alert while larger cores and radios sleep.

sample = sensor.read()

if cheap_gate(sample):
    features = dsp(sample)

    if confidence(features) > 0.82:
        result = local_model(features)
        buffer.append(result)

if useful(buffer) and radio_is_good():
    transmit(buffer)

Pseudo-code. The useful threshold and confidence policy belong to the product, not the model.

An imagined exploded view of a generic wireless earbud showing shell, battery, driver, microphones and circuit board

A COMPUTER INSIDE AN EAR

THE EARBUD IS ALREADY FULL.

Battery, driver, microphones, antenna, touch surface, seals and silicon share a few cubic centimeters and a temperature limit.

EXPLODED EAR-WORN DEVICEIMAGINED EDITORIAL IMAGE

05

RADIO

The wireless link is a shared, changing environment. The body is inside that environment.

BUFFER, COMPRESS, BURST

A RADIO SHOULD HAVE SOMETHING WORTH SAYING.

Batching reduces wake-ups. The cost is delay and the risk of losing buffered data. Pick the trade-off on purpose.

THE PERSON BLOCKS THE LINK

RANGE IS A POSTURE, A POCKET AND A ROOM.

A link budget on paper is the start. Antenna placement, orientation, absorption, multipath and coexistence decide the room.

LE AUDIO · LC3

THE CODEC CHANGES THE RADIO BILL.

7.5 msor 10 ms frames
< ½the SBC bitrate for comparable or better quality, in Bluetooth SIG listening tests

Lower bitrate can shorten radio-on time. Actual product power still depends on implementation, buffering, retransmission and RF conditions.

Source: Bluetooth SIG LC3 specification and LE Audio FAQ.

06

GLASSES

Put a computer on the face and every compromise becomes visible to the wearer and everyone nearby.

An imagined side profile of a person wearing subtle generic smart glasses in a city at night

THE FACE IS SOCIAL SPACE

CAPABILITY IS ONLY HALF THE DESIGN.

People around the device need to understand when it is sensing. The wearer needs to know what happened without opening an app.

CAMERA · AUDIO · SOCIAL SIGNALIMAGINED EDITORIAL IMAGE

THE OPTICAL NEGOTIATION

WIDEN ONE THING. PAY SOMEWHERE ELSE.

Near-eye display designs trade field of view, eyebox, image quality, brightness and product form. See Cholewiak et al., Optics Express, 2020.

A REAL PLATFORM ENVELOPE

SNAPDRAGON AR1 GEN 1

One current example of what smart-glasses silicon is being asked to integrate.

2image signal processors
8microphone support
3DoFhead tracking
1280²per-eye display support at 60 fps

Platform capabilities from Qualcomm's AR1 Gen 1 product page and product brief. A capability list does not describe battery life, thermal behavior or a finished product.

07

INTELLIGENCE

The architecture decides what the device can know, how fast it can respond and who else receives the data.

DRAW THE BOUNDARY

LOCAL AND REMOTE ARE PRODUCT BEHAVIORS.

Write the offline behavior before the network diagram. It exposes what the product really depends on.

THREE BILLS

EVERY INFERENCE PAYS IN TIME, ENERGY AND EXPOSURE.

Directional comparison. Workload, radios, caching and system design can move every cell.

CONTEXT NEEDS LAYERS

A LIVE STREAM IS NOT A MEMORY.

Compression should preserve provenance and uncertainty. Deletion needs to propagate through every layer.

MOST FAILURES ARE SYSTEM FAILURES

THE DEMO WORKS. THE DAY DOES NOT.

HOTsustained work ignored the thermal path
DEADidle current ate the battery
DEAFthe enclosure buried the microphone
SLOWevery useful action needs a round trip
CREEPYsensing state is invisible
FRAGILEthe happy path assumed perfect fit and RF

A DESIGN REVIEW FOR THE WHOLE DEVICE

ASK THESE BEFORE ADDING ANOTHER FEATURE.

  1. 01What is awake when nothing interesting is happening?
  2. 02What changes when fit, motion, light and RF get worse?
  3. 03Where does heat leave the enclosure?
  4. 04What still works offline?
  5. 05Can the wearer and a bystander see the sensing state?
  6. 06Can one person understand and delete what was kept?

THE ARCHITECTURE THAT SURVIVES

SPEND ENERGY ONLY AFTER A CHEAP SIGNAL EARNS IT.

SENSE LIGHTLY→DECIDE LOCALLY→WAKE SELECTIVELY→SHOW YOUR WORK

Small devices force honest architecture. The limits are useful. They make the product choose what matters.

SOURCES + IMAGE NOTE

READ FURTHER.

QualcommSnapdragon AR1 Gen 1 platform QualcommAR1 Gen 1 product brief Nordic SemiconductornRF54H20 product page Bluetooth SIGLC3 specification Bluetooth SIGLE Audio FAQ Pham et al.Wrist PPG and poor skin contact, 2025 Cholewiak et al.A perceptual eyebox, 2020

All photographs in this presentation are original, AI-generated editorial images. They are illustrative and do not depict a commercial product or engineering evidence. Technical diagrams are original and simplified.

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