How should I wear my device?

We recommend wearing your device on your non-dominant wrist, approximately two fingerbreadths above the wrist bone, during exercise. During general daily use, it can be worn one fingerbreadth above the wrist bone.

Figure 1.1

Figure 1.2

Figure 1.3

Figure 1.1 - 1.3. Device placement for all types of wearable devices during exercise

When the device is fitted too loosely around the wrist, the PPG sensors will lose contact with the skin. If there is a space between the sensors and the skin, the accuracy of the measurements can vary as the amount of light that reaches the sensors varies. In a lit environment, ambient light can introduce optical noise. In a dark environment, the amount of light that is reflected back to the sensor will vary depending on the movement of the LEDs and photodiodes relative to the skin. Furthermore, a loose fit will cause the device to move around on the arm too much, which can interfere with both the accelerometer and PPG signal. 

Similar to wearing it too loosely, wearing the device too far down the wrist (less than 2 fingerbreadths from the wrist bone) can introduce excessive movement of the device. Wearing the device on or too close to the wrist bone may also increase the amount of ambient light between the device and the skin, causing the PPG signal quality to degrade. This is exaggerated when performing activities with high wrist motion, for example, typing, driving, or weight lifting.

There are more capillaries beneath the surface of the skin higher up on the arm. This means that wearing the device further up the arm, away from the wrist, will improve signal quality and ensure accurate heart rate tracking. For this reason, we recommend wearing the device at least 2 fingerbreadths above the wrist bone, especially during exercise or activities with high motion.

It is also important not to fit the device too tightly as this will restrict the flow of blood under the sensor and contribute to a low signal quality. We suggest wearing your device tightly enough to fit snugly, but not so tight that it causes discomfort. Restriction of blood flow can also occur during sleep if additional pressure is exerted on the device, for example, when you sleep on your arm. Users with paler or lesser-pigmented skin tones are more prone to experiencing poor signal quality during sleep, so if you are fair-skinned and have a preferred side to sleep on, we recommend wearing your device on the opposite arm.

Figure 2. Device fit