Three wavelengths, three depths
Green 525 nm reads the pulse just under the skin. Red 660 nm and infrared 940 nm travel further, to the artery wall, and three photodiodes catch what scatters back.
250 samples / s
Reading now
58bpm
+0.18°C
Arc · 4.1 g · titanium grade 5
A ring that
reads the night.
Four wavelengths of light against the inside of your finger, sampled 250 times a second while you sleep. In the morning you get one honest number and the night it came from.
Look inside it- Battery
- 7 days
- Water
- 100 m
- Width
- 7.9 mm
Inside
Seven layers
in 2.55 mm.
- ShellGrade 5 titanium, bead-blasted then brushed by hand. 2.55 mm wall.
- Flex boardSix-layer polyimide, bent to a 9.6 mm radius after assembly.
- ChipsARM M33 core, BLE 5.4 radio, 6-axis IMU, NTC skin probe.
- CellCurved lithium-polymer, 22 mAh. Seven nights, 80 min to full.
- OpticsGreen 525 nm, red 660 nm, infrared 940 nm, and three photodiodes.
- LinerMedical epoxy, hypoallergenic, no nickel. Clear over the sensors.
Asleep
22:47
0 h 00 of 8 h 05
One night · Tue 13 Oct
The ring becomesthe clock of the night.
Every minute around the dial is one minute in bed.Long bars are deep sleep, the red runs are REM,and the thin outer trace is your heart slowing down.
- Deep 1 h 32
- REM 1 h 51
- Light 4 h 03
- Awake 0 h 39
Scrub the night
Move the needle
through eight hours.
Scroll, or drag along the strip below. The needle on the ring follows, and this is what the sensor saw in that minute.
Time01:47
StageDeep
Heart rate49 bpm
HRV (RMSSD)71 ms
Skin temp−0.21 °C
Breaths13.4 /min
Sleep score 84 · efficiency 92 % · lowest heart rate 47 bpm at 03:12 · in bed 22:41, out 06:58
What it reads
Five signals,
one finger.
Heart-rate variability
The milliseconds between beats, averaged every five minutes. Last night is drawn as an orbit round the ring: further out means better recovered.
68 msBlood oxygen
Red against infrared, every 30 seconds once you are asleep. The arc fills to the night's average; any dip under 90 % is flagged with its minute.
97 %Skin temperature
Against your own 30-night baseline, to 0.05 °C, painted onto the inner band: cooler blue, warmer red. The first hint of a fever, and of cycle phase.
+0.18 °CBreathing
Read from the rise and fall of the pulse wave, with no strap on the chest. The ring is breathing at the rate it measured.
13.4 / minSizing
Measure your finger.
Watch it fit.
Wrap a strip of paper round the base of the finger, mark the overlap and measure it. Type or drag that length: the ring resizes on the finger beside you.
mm
Your Arc size
US 8
Inner diameter 18.1 mm. A good fit for the index finger.
Pricing
Pay once,
or pay as you go.
Membership€ 511
Complete€ 449
Complete costs less from month 26 on.
- Charge cycles
- 156
- Battery health
- 93 %
- Firmware
- 4.6
- Membership
- trends · coach · damage cover
Order
Choose the finish.
Bead-blasted, then brushed by hand along the band. Takes on a soft polish where it meets the next finger.
- Size
- US 8 · index
- Plan
- Membership, € 5.90 / month
- Today
- € 299
Ships from 18 November. Free sizing kit if you are not sure. 60 nights to return it.