Hi there, it's Matt here and welcome back to the podcast and welcome back to another of our AMA episodes.

Ask Me Anything episodes. Let's really ask the two of us episode because it's myself and I am joined

as I always am by the brilliant mind of Dr. Etty Ben-Simon.

Eti, I always pronounce it in my own special way.

Welcome back to the podcast.

It's the best way to pronounce it.

Thank you.

So I think we've got lots of really fascinating questions, and we were just chatting very

briefly before we started recording to say, I need to do much better at getting through these

questions in a more direct, straight line, efficient, informationally rich, nevertheless,

manner, rather than going just long-winded. So let's see if we

can do that. Let us start with the first question. Okay, the first question. The challenge is on.

My sleep tracker says I get plenty of deep sleep, but I still feel exhausted. What could be happening here

and can we trust these devices? Yeah, it's a good question

and it's a question I do get asked a lot in the public about either which are the best devices

or are they accurate and what are the accuracies? Sleep trackers, whether they're in smart watch

form or a ring form or a headband sort of standalone device, just so people know,

they estimate sleep stages using a combination of different signals. And the sensors on these

different devices are measuring these different signals. So one of the sensors is what we

call an accelerometer and it measures movement. One of the other things

that they measure is your heart rate. So how quickly or slowly is your heart contracting? They also

measure the variability from one beat of your heart to the next. And that is called heart rate

...