Discretion. Power.

DISCOVER

The problem

You don't need another screen.

Smartwatches interrupt you all day. Fitness bands don't go with anything. And a fixed-size ring can't follow a body that changes.

Tetra gives you continuous health tracking, in a band you can wear anywhere, all the time.

The Tetra app: daily score, sleep, activity and heart rate

  • Smartwatch

    Screen

    It lights up, it buzzes, it never lets you forget it's there.

  • Smart ring

    Fixed size

    Your fingers swell, shrink, change with the seasons. It doesn't.

  • Fitness band

    Gym only

    It goes with nothing. You end up taking it off, and then it measures nothing.

  • Tetra

    No screen

    The same tracking, in something you don't want to take off.

  • A woman sleeping, wearing the Tetra band
    Sleep & recovery

    Get the best sleep of your life

  • A woman on the move, wearing the Tetra band
    Activity & movement

    Make every move count

  • A quiet moment, wearing the Tetra band
    Stress

    Get ahead of your stress

  • A woman wearing the Tetra band
    Heart health

    Listen to what your heart is telling you

  • The Tetra band in water
    Worn day and night

    Keep it on, day and night

  • The Tetra band on the wrist
    Share with someone you love

    Put the people who love you at ease

Made with care, for insights that go deeper

Designed like jewelry and built to be worn day and night, the Tetra band opens up real insight into your overall health: sleep, activity, stress, heart health and plenty more.

Meet the band

Your body, in plain English.

The inside of the Tetra band: optical sensor and circuit board

The Fitmo app is free for life, no subscription. Your readings, your daily scores and your trends are always there, on iOS and Android.

Heart health

Sleep & rest

Activity & movement

Stress

Recovery

Share with someone you love

Backed by the country's leading health experts

Fitmo's medical advisors guide what we measure, how the app explains it, and what every number is worth. Their combined clinical expertise makes it easier for hundreds of thousands of people to understand what their body is actually doing.

  • Board-certified

    25+ years experience in a medical specialty

  • Industry innovations

    40+ published studies in medical journals

  • Clinical oversight

    They defined what every score on your Tetra means

Dr. Melynda Barnes, MD

Dr. Melynda Barnes, MD

Chief Medical Advisor

Board-certified in cardiology, practicing for over twenty years

Stanford University School of Medicine
Yale School of Medicine
Dr. Raoul Manalac, MD

Dr. Raoul Manalac, MD

Sleep Medicine Advisor

Board-certified in sleep medicine and internal medicine

Johns Hopkins University
American Board of Obesity Medicine
Dr. Nitin Vaswani, MD MPH MBA

Dr. Nitin Vaswani, MD MPH MBA

Clinical Strategy

General practitioner and clinical researcher

University of Pennsylvania

Tetra isn't like other trackers

A piece of jewelry that tracks your health around the clock. No screen, no notifications, no subscription.

Tetra TETRA
The others THE OTHERS
What you're after
Understanding your body day to day, quietly
Athletic performance and step counts
Look
Jewelry that goes with everything, dinner included
A device you spot from across the room
Screen
None. Nothing buzzing on your wrist
Lit screen, alerts all day long
Fit
Adjustable clasp, follows a wrist that changes
Fixed size, measured and ordered in advance
Subscription
None. One purchase
$6 to $30 a month
Health tracking
Heart rate, blood oxygen, HRV, sleep stages, stress, recovery
Often just steps and a sleep score
Sharing with family
Included, with a QR code
Subscribers only, when it exists at all
Price
$129, once
$300 to $500 the first year, then every year after

You should be able to wear it without thinking about it

Most trackers announce themselves.

Tetra gets noticed too, for the right reason.

A module 5.6 mm thin.

0.4 oz on an adjustable clasp.

No screen, nothing lighting up in the middle of a conversation.

TetraTETRA :

"People compliment your bracelet. Nobody guesses it's a sensor."

The othersTHE OTHERS :

"A sports band you take off the moment you dress up."

A device you take off measures nothing. The best sensor is the one that stays on.

Your health data shouldn't come with a monthly bill

TetraTETRA :

One purchase. Free app for life. Your readings stay available, no conditions and no expiration date.

The othersTHE OTHERS :

$6 to $30 a month just to keep seeing your own data. Stop paying, stop seeing.

Do the math: a $6 a month subscription runs $216 over three years. That's more than the Tetra band itself, and you still own nothing.

Numbers about your health, not your performance

TetraTETRA :

Heart rate, blood oxygen, heart rate variability (HRV), deep, light and REM sleep stages, stress level and a recovery score. Continuously, day and night.

The othersTHE OTHERS :

Steps, calories, and a sleep score with no breakdown of the stages.

Tetra keeps recording even when your phone is in another room, and syncs everything the moment you pick it back up.

You look when you want. It never nags.

A band that alerts you all day ends up creating the very worry it claimed to settle.

Tetra takes the opposite approach.

No screen, so no alerts on your wrist.

Automatic detection lives in the app: turn it on if you want it, turn it off if it weighs on you.

And if you want someone close keeping an eye out, you add them with a QR code. Either direction, you decide.

It's your body. You choose when you look at it.

How does Tetra compare?
No screen, no notifications
Wears like jewelry
Adjusts to a wrist that changes
Health tracking
Share data with someone close
No subscription
3-year cost*
Tetra
Tetra
$179
Smart ring
Smart ring
Fixed size
Subscription required
Depends on brand
≈ $565
Smartwatch
Smartwatch
Sometimes
Depends on model
$250 to $800

The data you're after, in a piece of jewelry you won't want to take off.

* Tetra: one-time purchase, no subscription. Smart ring: $349 plus $5.99 a month over three years. Smartwatch: observed retail price range, excluding any optional subscription.

  • [FR] Bracelet Tetra dans ses trois finitions, argent, or rose et or vert
  • [FR] Bracelet Tetra or rose carmin porté au quotidien
  • [FR] Femme en mouvement portant le bracelet Tetra or rose
  • [FR] Bracelet Tetra argent sous l'eau, étanche 10 ATM
  • [FR] Bracelet Tetra or et vert impérial posé sur des pierres
  • [FR] Bracelet Tetra porté avec une tenue de ville
  • [FR] Bracelet Tetra or rose carmin porté au poignet
  • [FR] Barre pavée de cristaux du bracelet Tetra argent
  • [FR] Détail du pavage de cristaux du bracelet Tetra argent
  • [EN] The Tetra band in all three finishes: silver, rose gold and green gold
  • [EN] The rose gold Tetra band worn every day
  • [EN] Woman on the move wearing the rose gold Tetra band
  • [EN] Silver Tetra band underwater, water resistant to 10 ATM
  • [EN] Gold and imperial green Tetra band resting on pale stones
  • [EN] The Tetra band worn with everyday clothes
  • [EN] Carmine rose gold Tetra band worn on the wrist
  • [EN] Crystal pavé bar on the silver Tetra band
  • [EN] Close-up of the crystal pavé bar on the silver Tetra band
1 19

Hand-calibrated. Made in small batches.

Every Tetra is calibrated by hand by our technicians, so we keep production runs small on purpose — limit 2 per customer.

NEW
(450)

Tetra

What you feel is real.
Price going up
$249.90 $179.90

Tetra records what you feel but can't explain, day and night: your heart, your nights, your stress, your blood pressure trends. The app turns it into something you can actually read, there when you want it and not before. No screen, no notifications.

30-day money-back guarantee 30-day money-back guarantee
Free worldwide shipping Free worldwide shipping
Free app for life Free app for life
Ships by Ships by —
Offer available
48H:00M:00S
Gift not added to your order Valid through—
Finish: Argent Cristal
One payment. No subscription, ever. The app, every update and your data — yours for life.
In stock: Estimated
MONEY-BACK GUARANTEE 30 DAYS
Not sold after 30 days? You get every penny back.

Try Tetra at your own pace. Thirty days is also how long it takes for your first trends to show up. If it's not for you, send it back and we refund you in full, no questions asked.

« In my patients over 45, cardiovascular symptoms get written off as hormones or stress far too often. »

« What I see in the exam room is a woman describing fatigue that has settled in, sleep that has gotten worse, sometimes palpitations at night, and a perfectly normal workup. Having several weeks of heart rate and variability data gives the conversation somewhere concrete to start. It diagnoses nothing and replaces neither the exam nor the labs, but it steers my questions. »

Dr. Ana M.
Dr. Ana M.
Cardiologist, cardiovascular prevention
Verified review

What you feel, you can finally see

Your labs are normal and you still don't feel right. Tetra records what happens between appointments, so you show up with readings instead of a feeling.

Jewelry, not a gadget

No screen, nothing lighting up or buzzing. In a meeting, at dinner, in front of your kids, nobody can tell you're tracking anything. Only you know.

A clasp that follows your body

Your wrists aren't the same size depending on heat, water retention or the time of the month. Not a ring, not a rigid bangle: a slider that adjusts in a second, every day.

Continuous tracking that never interrupts you

Heart rate, HRV, blood oxygen, stress, sleep and blood pressure trends, day and night. No notifications. You open the app when you decide to.

Look out for someone, from a distance

The app lets you share your data with someone you choose, in either direction. A daughter can follow her mother. Sharing stops the moment you decide.

No subscription, and your data stays yours

One purchase, the app free for life. No feature behind a paywall, and your data never sold to anyone.

Tetra packs a multi-LED optical sensor and a three-axis accelerometer to measure your core data continuously. The app reads that data back to you as a clear picture of where your body is, day after day.

  • Heart rate, tracked continuously day and night
  • Heart rate variability (HRV)
  • Blood oxygen (SpO₂)
  • Stress level
  • Blood pressure trends (observational, not medical)
  • Detailed sleep: duration, efficiency, deep, light and REM stages
  • Physical recovery score
  • Physical and mental readiness score
  • Cycle tracking
  • Daily activity: steps, distance, calories
  • Water resistant to 10 ATM and a 5-day battery

From that data, the app helps you see your trends over weeks and understand what wears your body down and what builds it back. Tetra diagnoses nothing. It observes, and the conclusion belongs to your doctor.

1

Just wear it

Tetra wears like a bracelet, day and night. 0.4 oz, no discomfort, nothing to set up. The slider adjusts to your wrist in a second, and then you forget it.

2

Check your data when you decide to

No notification will come looking for you. You open the app in the morning with your coffee, or once a week. Your numbers are laid out plainly, with no jargon.

3

Watch your trends appear

After a few weeks, the patterns show up. The nights that count, the weeks that weigh on you, what brings your recovery back. These aren't impressions anymore.

4

Walk into your doctor's office with something

Several weeks of dated readings to put on the desk. You no longer say you've been tired for a while. You show them. And they draw the conclusion.

[PASTE A REAL REVIEW HERE, from your 450, ideally about how easy it was to get started]

First name L. — Verified customer
More information

The app is free for life for every Tetra owner. Works on iOS and Android, no subscription, nothing hidden behind a paywall.

You check your data when you decide to. You'll find your heart rate, your HRV, your blood oxygen, your stress level, your blood pressure trends, your nights in detail, your recovery and your cycle tracking.

It also includes sleep support, with an analysis of your night, suggestions, and a library of sounds to fall asleep to. And if you want, you can share your data with someone close.

Guided setup in a few minutes. And if your phone isn't nearby, the band keeps recording on its own: everything syncs the moment you reconnect.

Tetra was built for women who keep being told everything is normal. The labs are fine, people talk about hormones, stress, age, and yet something is off.

The problem isn't your doctor. It's that one blood test a year is a snapshot, while what you're living is a trajectory. Between two appointments, nobody is watching.

Tetra watches, continuously, with no screen and no notifications. Nobody can tell you're tracking anything, and nothing shows up to judge you or grade you. You open the app when you feel like it.

  1. Design: Jewelry format, no screen. Built to be worn day and night. Weight 0.4 oz, thickness 5.6 mm.
  2. Clasp: Sliding and adjustable, one size for every wrist. Adjusts in a second, every day.
  3. Finishes: Crystal Silver, Carmine Rose Gold, Imperial Green Gold. Fine materials, crystal-set bar and tennis chain.
  4. Band included: A second soft band, free, for workouts, sleep and water.
  5. Water resistance: 10 ATM, roughly 330 feet. Shower, pool and swimming.
  6. Sensors: Multi-LED optical sensor and three-axis accelerometer.
  7. Battery: 5 days. Full charge in 2 hours with the magnetic cable included.
  8. Connectivity: Bluetooth 5.3. Works with iOS 11 and Android 6 and up.
  9. App: Free for life on iOS and Android. No subscription, no paid features.
  • Heart rate, continuously, min, average and max
  • Heart rate variability (HRV)
  • Blood oxygen (SpO2)
  • Stress level
  • Blood pressure trends (observational, not medical)
  • Detailed sleep: duration, efficiency, deep, light and REM stages
  • Physical recovery score
  • Physical and mental readiness score
  • Activity: steps, distance, calories
  • Cycle tracking

No, and that's the whole point. Tetra has no screen. It's a jeweled band, with a crystal-set bar and a fine chain. In a meeting, at dinner, in front of your kids, nobody can tell you're tracking anything.

Yes, and every day of the year. Tetra isn't a ring or a rigid bangle: it's a band with an adjustable sliding clasp.

Your wrists aren't the same size depending on heat, water retention, hormones or the time of the month. A fixed size, picked on one given day, never works every day. One size, every wrist.

No. Tetra has no screen, so it can't show you anything, remind you of anything, or hold anything against you. It records, and you decide when you open the app.

If you'd rather it watch certain numbers automatically, that feature is in the app and you turn it on yourself. It's off by default.

Yes. The app lets you add someone and share your health and activity data, in either direction. A daughter can follow her mother's numbers, a spouse can follow their partner's.

Sharing works by invitation, and it stops the moment you decide.

Yes. Tetra is water resistant to 10 ATM, tested to roughly 330 feet. Shower, pool, swimming, no problem.

For chlorinated water and salt water, the free second soft band is ideal: nothing fazes it, and you keep the set finish looking bright. Rinse with clean water after swimming, like any piece of jewelry.

When your Tetra arrives, you'll find:

  • The Tetra band in the finish you chose
  • A second soft band, free*
  • A magnetic charging cable
  • A gift box
  • A clear quick-start guide

*While supplies last.

No. Tetra gives you estimates and trends to watch over time, so you can prepare for and get more out of your appointments. You show up with readings instead of a feeling. The interpretation and the conclusion stay with your doctor.

Yes. Fitmo is a French company and your data is:

  • Encrypted end to end
  • Hosted on European servers under GDPR
  • Accessible only by you, or the people you authorize

We never sell your data and we don't share it with any commercial third party. You can delete it permanently at any time from the app.

  • Processing: Orders are prepared within 1 business day.
  • Delivery time: 6 to 8 business days depending on your address.
  • Trial period: You have 30 days to try Tetra.
  • Returns: If it's not for you, the return is simple and no questions asked, for a full refund.

The band that gives you something to show

You were told it was hormones, stress, age. Your labs are normal and you still don't feel right. The problem is that between two appointments, nobody is watching.

  • See what stress and your nights are actually doing to your body
  • Follow your blood pressure trends, day after day
  • Walk into your doctor's office with readings, not a feeling
View full details

What women who wear Tetra have to say.

Also from Fitmo

There's one for him, too.

The Vitro is the other Fitmo band. Same idea, no screen and no subscription, in a build made for a man's wrist. It's the one people buy for a husband or a dad.

Vitro, the Fitmo smart band, in black, silver and champagne gold Meet Vitro

Frequently asked questions

No, and that's the whole point. Tetra has no screen. Nothing lights up, nothing buzzes, nothing grades you in the morning.

It's a jeweled band, with a crystal-set bar and a fine chain. In a meeting, at dinner, in front of your kids, nobody can tell you're tracking anything. Only you know.

Continuously, day and night:

  • Heart rate (min, average, max)
  • Heart rate variability (HRV)
  • Blood oxygen (SpO2)
  • Stress level
  • Blood pressure trends (observational, not medical)
  • Detailed sleep: duration, efficiency, deep, light and REM stages
  • Physical recovery score
  • Physical and mental readiness score
  • Activity: steps, distance, calories burned
  • Cycle tracking

You don't enter anything. You wear it, it records.

Yes, and every day of the year. Tetra isn't a ring or a rigid bangle: it's a band with an adjustable sliding clasp.

Your wrists aren't the same size depending on heat, water retention, hormones or the time of the month. A fixed size, picked on one given day, never works every day. The slider adjusts in a second, without you thinking about it.

One size, every wrist.

No. That's a design decision.

Tetra has no screen, so it can't show you anything, remind you of anything, or hold anything against you. It records, and you decide when you open the app.

If you'd rather it watch certain numbers automatically, that feature is in the app and you turn it on yourself. It's off by default.

Yes. The app lets you add someone and share your health and activity data, in either direction.

In practice, a daughter can follow her mother's numbers, a spouse can follow their partner's. Sharing works by invitation, and it stops the moment you decide.

It's the feature most people pick when they buy Tetra as a gift rather than for themselves.

No, never. You buy the band once, and you get every feature and all of your data for life through the free app.

No hidden fees, no monthly charge, no feature locked behind a paywall. Your data belongs to you.

For comparison, a leading smart ring runs about $349 plus $5.99 a month. Over three years, that's more than $560.

Yes. Tetra is water resistant to 10 ATM, tested to roughly 330 feet. Shower, pool, swimming, no problem.

Like any piece of jewelry, rinse it with clean water and dry it after the pool or salt water. It keeps the finish bright over time.

  • 5 days of battery depending on how you use it
  • Full charge in about 2 hours with the magnetic cable included

The easiest thing is to charge it while you shower or get ready. Two hours is enough, and you don't miss a single night, which is exactly when it does the most work.

Yes. Every morning, the app turns your data into a plain reading, with concrete recommendations instead of a wall of graphs.

It also includes sleep support: an analysis of your night, suggestions, and a library of sounds to fall asleep to.

And daily goals you set yourself, if you want them.

Tetra works with:

iOS

  • iOS 11.0 and up

Android

  • Android 6.0 and up

Syncing happens over Bluetooth with the free app, on the App Store and Google Play. If your phone isn't nearby, the band keeps recording on its own and your data syncs the moment you reconnect.

No. Tetra gives you estimates and trends to watch over time, so you walk into your appointments with more to go on.

That's exactly where it helps: between two visits, nobody is watching. You show up with readings instead of a feeling. The interpretation and the conclusion stay with your doctor.

You get 30 days to try your Tetra, no strings attached. If it's not for you, send it back and we refund you in full, no questions asked.

Thirty days is also how long it takes for your first trends to show up. It's enough time to judge it, not just to make up your mind.

Yes. Fitmo is a French company, and your data is:

  • Encrypted end to end
  • Hosted on European servers under GDPR
  • Accessible only by you, or the people you authorize

We never sell your data and we don't share it with any commercial third party. You stay in full control at every step, and you can delete everything permanently from the app at any time.

Tetra
Tetra $179.90$249.90