Hi, you're about to get smarter in just a few minutes with Curiosity Daily from

Curiosity.com. I'm Cody Goff. And I'm Ashley Hamer. Today you learn about which

sleep trackers are actually accurate and how important closure is for a life transition.

We'll also answer a listener question about why mirrors flip horizontally but not vertically.

Let's satisfy some curiosity. If you want to track how much you sleep,

you might try a wearable sleep tracking device.

But how precise are those devices really?

That's what a group of neuroscientists from West Virginia

University wanted to find out. And if you use a sleep tracker, like I do, the

answer may be bad news, depending on the tracker you use.

For this study, the team tested nine different commercial sleep trackers to see which ones actually worked.

And they found that a lot of sleep trackers either over or underestimate the number of

winks you get per night.

For 98 separate nights, they had five healthy adults sleep while they were hooked up to both commercial sleep trackers and an EEG device.

That's a device that measures the brain's electrical activity and it's a really accurate way to monitor a person's sleep stages.

The researchers looked at total sleep time, total wake time, and sleep efficiency.

That's how long a person slept versus how long they were in bed. So what did they find? Well, when

it comes to how long the participants slept, the best performers were the Fitbit Ionic

and the ORA Smart Ring. All the other devices either

underestimated or overestimated sleep time, wake time, or sleep efficiency. But none of the

commercial sleep devices could accurately detect when participants were experiencing REM or non-rem sleep,

even though many devices claim to.

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