Gold electrodes ×2
Bioimpedance and sweat activity share the same two contacts, sampled in different modes.
HB-1 · Smart hydration ring
Hydration is the one thing your wearable still cannot tell you.This one can.
Five sensors read fluid levels through your finger, all day, with nothing to stick on and nothing to remember. One number, and one instruction: how much to drink, and by when.
Free sizing kit ships first. No subscription, ever.
HB-1 · Interactive model
HYDRATION LOW · DRINK 400 ML
The landscape
Hydration sensing already exists.
None of it stays on.
This is the honest version of the competitive picture, and it is a better argument than pretending nobody got here first. Three approaches are on the market. Each one works. Each one stops working the moment you forget about it.
Sweat patches
Nix, Gatorade Gx
Microfluidic adhesive patches that read sweat chemistry during exercise. Genuinely good science, validated in athletes, and the closest thing to a real measurement on the market.
Single use. They only read while you are actively sweating, and every session costs another patch.
Spot-check bioimpedance
AURA Strap
An Apple Watch band that runs bioimpedance to estimate body water. Same underlying method HydroBand uses, and proof the measurement can be miniaturised.
You open an app and hold your palm to the band for about 30 seconds. Nothing is measured unless you decide to measure it.
Continuous, on your hand
HydroBand HB-1
Bioimpedance and sweat sensing on a ring that is already on your finger for sleep and heart rate. Sampled through the day, with no patch, no consumable, and no scan to remember.
The trade is battery. Five to seven days, against eleven or more for rings that measure less.
COMPETITOR CAPABILITIES SUMMARISED FROM PUBLISHED PRODUCT DOCUMENTATION AND INDEPENDENT REVIEWS, JULY 2026.
How it works
Your finger is the best place
to measure this.
Fingers are dense with capillaries and sweat glands. A ring also holds its sensors flat against skin far more consistently than a watch band does, because a ring cannot slide. That is the whole reason this is a ring.
01 · SENSE
Five sensors, all day
Two gold electrodes measure bioimpedance and sweat activity. An optical sensor reads heart rate and variability. A thermistor tracks skin temperature. A 6-axis motion sensor catches workouts.
02 · LEARN
Fourteen days to a baseline
A one-minute setup survey seeds the model. Two weeks of wear teaches it your resting fluid level, your typical sweat rate, and how fast you come back after a hard session.
03 · SCORE
One number
A model on your phone combines the sensor data with your workouts and the local weather into a score from 0 to 100. It reports movement against your own baseline rather than an absolute body water figure, which is the part the science actually supports.
04 · ACT
An instruction, not a nudge
"Drink 400 ml in the next 30 minutes." If your phone is out of range, the ring runs a smaller model on its own hardware and flashes the light band.
Bioimpedance
Sweat activity
Heart rate
Skin temperature
Motion
The app
It answers one question.
Should I drink right now? Every other screen exists to make that answer accurate.
HomeYour score and the current instruction.
TodayThe score through the day, sweat loss per workout, two-tap logging.
TrendsWeekly averages, baseline drift, and where your low windows fall.
RingBattery, light alerts, offline buffer, water lock.
Press Alert on the model above, then look back at the phone. The light band and the app change together, which is how the real pairing behaves.
Good afternoonRING 64%
68HYDRATION
On track · 6% under your baseline
250 ml by 3:30 PMWarm afternoon, and you ran this morning. Sip it, do not chug it.
Drink 400 ml nowBioimpedance down 9%. Sweat rate high. Resting heart rate up 7 bpm. Recheck in 30 minutes.
1.4 LTODAY
620 mlSWEAT EST
717-DAY AVG
TodayWED · JUL 8
6 AMNOONNOW
Run · 5.2 km11:04 AM · 34 min
−620 MLDOUBLE-TAP THE RING TO LOG HANDS-FREE
TrendsLAST 7 DAYS
Weekly average: 71. Your baseline drifted down 2% during the heat wave, which is normal. Your worst window is 2 to 5 PM. A standing 300 ml at lunch would flatten it.
Saturday read low all afternoon. Salt water masks sweat readings, so the score leaned on bioimpedance instead.
RingHB-1 · SIZE 10
Battery64% · 3 DAYS LEFT
Light alertsRed pulse when you run low, phone or no phone
Offline bufferBaselines and alerts with no phone in range
14 DAYSWater lockEngages below 1 metre
AUTODouble-tapLogs 250 ml
FirmwareUpdated 2 July
v1.4.2Interactive · tap the tabs
Engineering
Everything fits in 2.7 millimetres.
A 22 mAh curved cell spans 140 degrees of the band. A flex circuit carries the compute around the rest. Then the cavity is filled solid with epoxy, which is also the waterproofing. Switch the model above to Inside to see the layout.
The battery is the entire design constraint. Bioimpedance runs on a fifteen-minute duty cycle instead of continuously. That is the difference between five days and two.
22 mAh curved cell
Five to seven days at roughly 0.6 grams. It sets the sampling budget for every sensor on the board, and it is the reason this ring lasts a week instead of two.
Bluetooth 5.3 SoC
Radio and microcontroller in one package. It also runs the small threshold model that fires alerts when your phone is not around.
BIA and EDA front end
Drives a microcurrent through finger tissue and reads what comes back.
Optical module
Resting heart rate climbs and variability drops as fluid falls. This catches both.
NTC thermistor
Skin temperature, pressed against the inner liner for heat strain context.
6-axis motion sensor
Detects workouts, and reads the double-tap that logs a drink.
16 MB flash
Holds your baselines and buffers two weeks of readings. Capacity is not the limit here. Policy is.
Two-track charge pads
Concentric gold contacts on the bottom edge meet two pogo pins in the case. The ring docks at any rotation, so there is no alignment to get right. No port and no coil.
Titanium and epoxy
A grade 5 titanium shell over a fully potted medical grade epoxy interior. It is the same construction the category has settled on, and it is why a ring with no openings can be rated to 100 metres.
Specifications
The full sheet.
Build
Grade 5 titanium shell, medical grade epoxy interior, 3.9 g at size 10
Dimensions
8.0 mm wide, 2.7 mm thick, US sizes 6 to 13
Bioimpedance
Two gold electrode bands, 15-minute duty cycle, reported as change against your own baseline
Sweat activity
Electrodermal sensing on the same electrode pair, continuous during activity
Heart
Optical heart rate and variability, palm side of the band
Temperature
NTC thermistor against the inner liner
Motion
6-axis accelerometer and gyroscope, workout detection, double-tap gesture
Battery
5 to 7 days typical, 22 mAh curved cell. Heavy training days land at the low end. Full charge in 45 minutes.
Charging
Any-angle two-track contacts. The case charges over USB-C and holds five full recharges.
Water
100 metres. No external openings anywhere on the ring. Water lock engages automatically.
Offline
14-day buffer on the ring, with light band alerts from stored baselines
Connectivity
Bluetooth 5.3 LE, iOS and Android
Price
$250, and nothing after that
| Ring | Hardware | Subscription | Three-year cost | Battery | Hydration |
|---|---|---|---|---|---|
| HydroBand HB-1 | $250 | None | $250 | 5 to 7 days | CONTINUOUS |
| Oura Ring 4 | From $349 | $5.99 / month | About $559 | 5 to 8 days | None |
| Samsung Galaxy Ring | $399 | None | $399 | Up to 7 days | None |
| RingConn Gen 3 | About $349 | None | About $349 | 11 to 14 days | None |
| Ultrahuman Ring AIR | About $349 | None | About $349 | Up to 6 days | None |
PRICING AND SPECIFICATIONS COMPILED FROM MANUFACTURER DOCUMENTATION AND INDEPENDENT REVIEWS, JULY 2026. OURA THREE-YEAR FIGURE IS $349 PLUS THIRTY-SIX MONTHS OF MEMBERSHIP AT THE ANNUAL RATE. RINGCONN AND ULTRAHUMAN PRICES MOVE OFTEN. CONFIRM BEFORE ANY EXTERNAL USE.
For investors
A measurement with no default owner.
Hydration sensing is real and it works. What it has never been is passive. Every product that measures it well asks the user to do something first: apply a patch, open an app, hold still for thirty seconds. We are betting the category is won by whoever removes that step, not by whoever invents the sensor.
Market$1.1B to $2.5B
Smart ring forecasts disagree sharply. Mordor Intelligence puts the category at $0.41B in 2025 reaching $1.14B by 2030. Other houses project as high as $2.5B. Growth rates cluster between 23 and 25 percent, which is the number worth trusting.
Price$250, direct
A hundred dollars under the rings people actually cross-shop, with no recurring fee. Oura runs about $559 over three years. We ask for $250 once, and never again.
Recurring revenueTeams · $99 a seat
Subscription belongs where somebody else signs the cheque. Fleet dashboards for industrial heat safety, college athletics, and defence, billed per seat per year.
Why the timing works
In January 2026 the FDA replaced its 2019 general wellness guidance. The revised policy states plainly that noninvasive products which sense or infer physiologic parameters can sit inside general wellness, provided they avoid diagnostic claims and do not substitute for a cleared device. HydroBand is noninvasive and suggests fluid intake. That is a clearer regulatory path than this product had eighteen months ago, and it is the single largest reason to build it now.
Unit economics
| Cost line | First run · 25k units | At volume · 100k units |
|---|---|---|
| Electronics | $28 | $22 |
| Battery and flex circuit | $12 | $9 |
| Titanium shell and moulding | $23 | $17 |
| Assembly, potting, QA | $12 | $9 |
| Charging case | $14 | $11 |
| Packaging and sizing kit | $4 | $3 |
| Cost of goods | $93 | $71 |
| Gross margin at $250 | 63% | 72% |
Cost of goods is not the whole ledger, and pricing off it alone is how hardware companies quietly bleed out. Here is what happens once acquisition, fulfilment, and warranty are in the model.
What is left per ring
| Line | First run · 25k units | At volume · 100k units |
|---|---|---|
| Retail price | $250 | $250 |
| Cost of goods | ($93) | ($71) |
| Gross profit | $157 · 63% | $179 · 72% |
| Customer acquisition | ($70) | ($55) |
| Returns and warranty reserve | ($15) | ($12) |
| Shipping, fulfilment, sizing kit return | ($12) | ($9) |
| Payment processing | ($8) | ($8) |
| Support | ($5) | ($4) |
| Contribution per ring | $47 · 19% | $91 · 36% |
We priced this at $150 first. Then we built the lines underneath cost of goods and found we were losing about forty-three dollars on every ring at first-run volume, and barely breaking even at a hundred thousand. $250 is not a confidence play. It is the number the model actually supports, and it still lands a hundred dollars below the ring people cross-shop it against.
What could kill this
The sensing does not hold up
Whole-body bioimpedance runs electrodes hand to foot. We are reading a single finger, which is a much shorter path and a noisier one. The literature also shows bioimpedance tracks change in hydration better than it measures an absolute figure, and there is still no agreed protocol for assessing hydration in athletes. That is why the score is relative to your own baseline, and why the validation study is the first thing we fund rather than the last.
Oura's patents
This is the risk most new entrants underprice. Ultrahuman's Ring AIR is under a US import ban following its patent dispute with Oura, and RingConn settled by taking a licence. Any ring we ship in the United States needs a freedom-to-operate review and a licensing budget before tooling, not after.
A fast follower
Oura or Samsung can add an electrode pair to the next revision. The hardware was never the moat. The labelled dataset and a two-year head start are, and both of those expire.
Acquisition cost
Seventy dollars to win a customer is an estimate, and direct-to-consumer hardware routinely comes in worse. Every ten dollars it slips takes four points off contribution, so at a hundred and twenty dollar acquisition cost the first run stops contributing anything. Battery is the other exposure: five to seven days sits below where the category has moved, and reviewers will say so.
Three years
YEAR 1Ship HB-1
A 25,000-unit first run sold direct at $250. Freedom-to-operate review closes before tooling. The university validation study runs in parallel and gets published either way.
YEAR 2HydroBand Teams
Fleet dashboard at $99 per seat per year. First pilots in industrial heat safety and college athletics convert to contracts.
YEAR 3Scale and license
A 100,000-unit run takes gross margin to 72 percent and contribution to roughly 36. Licensing conversations open for the sensing stack.
MARKET FIGURES FROM PUBLISHED THIRD-PARTY FORECASTS, JULY 2026. COST LINES ARE ESTIMATES BUILT FOR THIS PRESENTATION AND ARE NOT VENDOR QUOTES. REGULATORY SUMMARY IS NOT LEGAL ADVICE.
Questions
Before you ask.
Is HydroBand a medical device?
No. It suggests fluid intake and does not diagnose dehydration. The FDA's revised general wellness guidance, issued in January 2026, addresses noninvasive products that sense physiologic parameters directly, and HydroBand is written to sit inside it. We are careful about this wording everywhere, including in the app.
How accurate is it?
Bioimpedance tracks change in body water better than it measures an absolute amount, and clinical work uses electrodes placed hand to foot rather than around one finger. HydroBand reports movement against your own baseline for exactly that reason. A university validation study is budgeted for the first year and the results get published whichever way they land.
How is this different from a sweat patch?
Patches from Nix and Gatorade read sweat chemistry well, but they are single use and only work while you are actively sweating. HydroBand runs on a ring you already wear, through the whole day, including the hours before a session when the deficit actually builds.
Can I swim with it?
Yes. Rated to 100 metres, which covers showers, pools, saunas, and open water. The ring has no ports or openings at all. The charging case is not waterproof.
Why is the battery shorter than other rings?
Because it is doing more. Bioimpedance and electrodermal sensing both cost power that a sleep-focused ring does not spend. Five to seven days is the honest number, and heavy training weeks land at the low end.
What happens if I leave my phone at home?
The ring stores two weeks of readings and runs a smaller model on its own hardware. If you drop below your threshold, the light band flashes red until you acknowledge it with a double-tap.
Do I need a subscription?
No. The score, the alerts, and your full history come with the ring. The subscription tier is sold to organisations, not to you.
How do I get the right size?
A free sizing kit ships first with eight plastic rings. Wear one for a full day, since fingers swell, then send the kit back in the prepaid envelope. Fit matters more here than on a watch, because a loose ring breaks sensor contact.