Sizing & Fit
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Fit affects accuracy more than anything else. The sensor reads light through your skin, so if there's a gap between the device and your wrist, readings go patchy. Snug but not tight, sitting flat, about a finger's width above the wrist bone.
The Air is one size and adjusts to fit, and it comes with two straps in the box - a woven one and a silicone one. There's nothing to measure before you order.
Where to wear it
On the top of your wrist, a finger's width above the wrist bone, with the sensor sitting flat against the skin. Not on the bone itself, and not down on the hand side of it - both leave gaps.
Either wrist works. Most people wear it on the non-dominant one because it gets knocked about less and moves less during the day, which gives steadier readings.
How tight it should be
Tight enough that it doesn't slide when you turn your wrist over, loose enough that you can just get a fingertip underneath.
- Too loose shows up as gaps in your heart rate, missing sleep, and step counts that look low.
- Too tight leaves a mark, gets uncomfortable after an hour, and doesn't make readings any better.
If you've had it on for a while and there's a deep line in your skin when you take it off, go a notch looser.
Putting on the woven strap
The woven strap fastens with hook and loop. There's no buckle.
- Feed the tail through the metal loop and pull it all the way back through.
- Pull it back on itself until the strap is snug, with the module on top a finger's width above the wrist bone.
- Press the tail down flat onto the strap so the hook and loop grips.
Press it down along as much of its length as you can rather than just the end, since a tail fastened only at the tip is the one that lifts and catches on a sleeve.
Putting on the silicone strap
The silicone strap works like a watch strap. Push the pin through whichever hole sits right, then tuck the tail under the keeper loop so it lies flat.
Go one hole tighter than feels obvious. Silicone has no stretch, so a hole that feels perfect standing still will be loose the moment you move.
Which strap to use
- Woven for everyday wear and for sleeping. It's softer against the skin overnight.
- Silicone for swimming, showering and anything wet. It doesn't absorb water, it wipes dry, and it's ready to put back on straight away.
Swapping the straps
The strap loops straight through the module. Slide the one you're using out of the slots on either side, then feed the other one through the same way and check it's sitting flat before you put it on.
Wearing it for exercise
Move it an inch or two further up your arm and tighten it by one notch before you train. Wrist movement during weights, boxing and anything with a grip is the main cause of dropped heart rate readings. Loosen it again afterwards.
Wearing it in bed
Keep it at the same tightness you wear it during the day. People often loosen it for comfort at night and then wonder why their sleep data has gaps in it. If it's uncomfortable to sleep in at daytime tightness, it's probably too tight in the daytime too.
If it marks or irritates your skin
Almost always moisture and friction rather than the materials themselves.
- Loosen it slightly and move it a centimetre or two up or down your wrist.
- Switch to the other strap for a few days. Some people get on better with woven, some with silicone.
- Take it off after workouts and let both your skin and the strap dry properly.
- Rinse the strap in clean water if you've been sweating in it, and let it dry fully before putting it back on.
- Give your wrist a break for an hour or two a day.
If irritation carries on after all that, stop wearing it and speak to a pharmacist or your GP. Get in touch with us too and we'll sort a different strap out.
It won't fit
Between the two straps most wrists are covered, but if both are at the end of their adjustment, message us with your order number and your wrist measurement and we'll try our best to sort one that fits.
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