The biometric tracker that clips behind your watch.
2.4 mm thin. It reads heart rate, HRV, sleep, skin temperature and SpO₂ from under the watch you already wear.
Turn it over.
Steel, titanium, gold or ceramic. Flat or exhibition caseback, 34 to 46 mm across.
SubDial clips behind the lugs.
Three spring arms on soft pads. No adhesive, no marks, off again in a second.
Wear it. That is all.
It reads all day and overnight, 7 days to a charge, and syncs whenever your phone is near.
A band means a second wrist. A ring means a size, and taking it off to lift. A caseback means the watch you chose, with the data you were missing.
SubDial reads the same signals a band or ring reads, from the underside of the wrist where the caseback already sits, and exports every reading to Apple Health or Health Connect.
Eight readings, each on its own subdial.
Every needle is drawn to the scale it measures, at a typical night’s values. The app shows the same dials with your own numbers.
Fits casebacks
from 34 to 46 mm.
Set the arms. Turn the ring until the three arms open to your case size. Marks on the ring read 34 to 46.
Seat it. Place the disc on the caseback and let go. The arms close behind the lugs on soft polymer pads. Nothing else touches the case.
Wear it. Pair once in the app. The disc sits where a band’s sensor would, against the underside of the wrist, and comes off in a second to switch watches.
SubDial S1 specifications
- Disc
- 28 mm across, 2.4 mm thick4.1 g with arms
- Fit
- Casebacks 34 to 46 mmFlat or lightly domed, exhibition backs included
- Materials
- Grade 5 titanium ring, sapphire windowTPU pads on all three arms
- Water
- 5 ATMShower and swim. Not for diving.
- Battery
- 7 days typical45 minutes to full on the magnetic coin
- Memory
- 14 days on the disc
- Optical
- 3 green, 1 red and 1 infrared LED, 2 photodiodesHeart rate, HRV, SpO₂, respiratory rate
- Thermal
- Skin temperature, ±0.1 °C
- Motion
- 6-axis accelerometer and gyroscopeSleep staging, activity, automatic workouts
- Radio
- Bluetooth LE 5.3
- App
- iOS 17 and Android 12 or laterApple Health and Health Connect export, CSV download
- Status
- Pre-productionEvery figure on this page may change before shipping
Reserve a SubDial for $0.
Free and refundable. The first batch ships spring 2027 in order of reservation. You get one email when it is your turn to order.