30mm disc slipped beneath the case of your favorite analog watch is the latest pitch to solve a familiar dilemma: wearing a classic timepiece without missing out on modern fitness tracking. Health-monitoring wearable startup Azume has launched crowdfunding for the Azume One, a sensor puck designed to sit between your existing non-smart watch and your wrist. Instead of strapping on a glowing screen or wearing two devices at once, you get health tracking tucked underneath what you already own. In our view, it sounds like an elegant escape from bulky smartwatches, but the physics of tiny hardware quickly catches up with you.
Can a miniature disc really deliver full fitness tracking without ruining the comfort of a traditional watch? The short answer is yes, provided you are ready to accept daily charging routines and modest water protection.
The Screenless Sensor Under the Case
The hardware itself focuses entirely on background measurement. Azume packed the Azume One with a photoplethysmography sensor for tracking pulse rate and blood oxygen concentration, alongside an inertial measurement unit and a temperature sensor.
"You picked your watch for a reason. Maybe it was a gift. Maybe you saved for it. Maybe it just feels like you," as Azume's Ferdinand Schnagl stated of the thinking behind the company's product. "But if you want to understand your body, the market gives you two options: take your watch off and replace it with a smartwatch, or wear two devices at once. Most trackers also come with a screen that keeps lighting up, notifications that keep pulling you back to your phone, and a monthly subscription that never ends. We thought there had to be a better way. So we built a tracker you never see."
By stripping out the display, the sensor puck gathers metrics like heart rate variability, skin temperature, and sleep stages silently in the background. The setup keeps your wrist looking entirely traditional while routing all your body metrics directly to your phone. But how does cramming all those sensors into a coin-sized puck affect daily usability?
The Battery and Water Compromise
The trade-off lands squarely on battery life and durability. To keep the sensor thin enough so it does not lift your watch awkwardly off your wrist, the battery capacity had to stay minimal. According to the assessment of Azume, a single 30-minute charge delivers up to 48 hours of usage, which means you will be taking it off to charge every couple of days despite the total absence of a power-hungry screen.
In fact, anyone expecting a rugged sports companion will be disappointed. The device is rated strictly as sweat, rain, and hand-washing resistant rather than truly waterproof, making it unsuitable for swimming. For gym sessions where you might leave your expensive mechanical watch in a locker, the company also offers an accessory band so you can wear the bare sensor puck alone.
What This Costs on Kickstarter
If you want to back the project, the Azume One is currently funding on Kickstarter with physical rewards starting at €109, which converts to roughly $122. Hardware is expected to ship in December this year.
If you wear an analog watch every day and refuse to swap it for a glowing slab of glass, backing the Azume One for around $122 gives you unobtrusive metrics. Just prepare for a 48-hour charging rhythm and remember to take it off before jumping into the pool.
What came before
Combining classic wristwatches with smart tracking used to mean wearing two bands on both wrists, but the Azume One sensor now sits directly underneath the watch case itself. Eliminating the display and dodging bulky smartwatches comes with noticeable compromises in battery life and durability. Azume packed optical and temperature sensors into a tiny disc, yet its miniature battery needs recharging every two days. Will Azume manage to win over classic watch lovers when a €109 sensor has to be taken off before every swim?