Note: The optical heart sensor provides the best data with resting heart rate above 30 beats per minute and exercising heart rate above 90 beats per minute. In addition, the optical heart sensor is designed to compensate for low signal levels by increasing LED brightness.

Getting accurate and consistent heart rate readings from your Smart Swim 2 goggles will depend on a number of factors. 

1. Fit

The first and most important is fit. When you first receive your goggles, you should go through the Fit Guide and process here (Getting the right fit) to ensure that the sensor sits snug against your temple and doesn't move around when you are swimming. If the fit isn't correct, not only will you experience discomfort or leaking during your swim but you will also notice that the heart rate data isn't tracked correctly. 

2. Sensor cleanliness

Over time, the sensor can accumulate dirt and debris from things like lotions, pool chemicals and water residues. Ensuring that the sensor is clean will allow for the clearest heart rate readings. We recommend following the cleaning instructions here for best results: How do I clean and maintain my goggles?

3. The HR Check screen

Before starting your swim, you will see a screen in the goggles which will check that your heart rate is coming through. If you don't see a value on this screen, or the goggles indicate to check your placement of the HR sensor, this is a good indication that there's a fit issue. Check that there are no obstructions between the sensor and your skin, and that the sensor is snug against the skin with no gap.

4. Temperature

The temperature of your body and of the environment will affect how easily your heart rate is picked up. If you are cold, then your blood vessels will constrict to preserve your body temperature. This makes it harder for the sensor to pick up your heart rate. If you are cold when entering the water, allow some time for your body to warm up slightly before starting your swim activity.