Getting a good night’s sleep is about more than just the number of hours from when your head hits the pillow to when you wake up. “Generally people aren’t the best judges of how long they’ve actually slept or whether it was quality sleep,” says Dr. Conor Heneghan, a senior staff research scientist on Google’s consumer health research team. That’s where wearables like Fitbit can come in handy.

Our devices equipped with heart rate sensors (like a Charge 6 or Pixel Watch 2) track your heart rate while you sleep and record it in your Fitbit app to help you learn more about your habits. Your heart rate is also a key input for many other helpful insights and tools available within the Fitbit app, like your Sleep Insights, Sleep Stages, and Sleep Score, as well as Daily Readiness and Sleep Profile, which are part of a Fitbit Premium subscription. You can use this data to help you understand how well — not just how long — you slept. Then, if you notice that your sleep hygiene could use some help, you can make a few changes to your habits to improve your sleep quality, like watching your stress levels, reducing your alcohol intake and skipping late-night workouts, says Dr. Heneghan.

Looking for a way to help you tackle those restless nights and groggy mornings? Here are three reasons to start tracking your heart rate while you sleep.

1. It can tell you whether you’ve gotten enough deep sleep.

When you’re sleeping, your body goes through several types of sleep stages through the night — light, deep and rapid eye movement (REM) — and how long you stay in each stage can affect the quality of your sleep. “To feel refreshed in the morning, you want about 15-20% of your night’s sleep to be deep sleep,” says Dr. Heneghan. When you wake up in the morning, use the Sleep Stages tool in the Fitbit app to see how much time you spent in each stage of sleep the previous night.

2. It can tell you how restorative your sleep is overall.

A lower heart rate during different periods of your sleep throughout the night can indicate whether or not your sleep has been restorative. This means that you’re sleeping deeply enough for long enough that your body and brain can get to the important work of muscle repair, tissue growth, and a number of other critical processes that support your brain function and overall health.

“Ideally, your heart rate when you’re sleeping should be lower than your resting heart rate when you’re awake to enable that restorative rest,” says Dr. Heneghan. Try measuring your heart rate with your Fitbit when you first wake up — before you get out of bed — to get a sense of your baseline resting heart rate. Then, compare that with your sleeping heart rate data. “When you’re in periods of deep sleep, you should see a low heart rate with not much variation. If on the other hand, you see a higher heart rate than normal for you during sleep, or a lot of variability or spikes in your heart rate, that can indicate a more restless night resulting in a less restorative sleep,” he says. If you have a Fitbit Premium subscription, you can also check your Restoration Score in the Fitbit app to see how restful your sleep was.