Turns out there's more to measuring your sleep than just counting sheep.
In the past year or so, a handful of new devices have come on the market that promise to help you measure your sleep quality, learn when your good night goes bad, and even wake you up at the optimal time. They come in a range of guises, but they're all the result of two trends: sleep research that has given scientists a new understanding of what constitutes a good night's sleep, and cheaper, better sensors that make these tools affordable and easy to use.
Before I drill down into the devices, a bit of context on the benefits and science of tracking our sleep. I've written earlier here at HuffPost about the promise of self-tracking for improving our health -- and sleep is no exception. The premise of monitoring our sleep is a bit tricky, though, since we're, uh, supposed to be asleep. So we need to use sensors and proxies to measure things that we hope correspond to sleep quality through the night. Most of this boils down to measuring how long we spend in the five phases of sleep, from light sleep to REM to deep sleep.
The traditional approach to sleep research is called polysomnography, an intensive high-fidelity approach that typically requires more than 20 wires to be hooked up to the test subject. This noodle soup of nodes and cables measure everything from eye movement to leg movement to breathing and heart rate. This is the stuff of sleep labs, and though the measurements are highly detailed and thorough, they come with a catch: By requiring somebody to go to a sleep lab to be measured, your inherently messing up the experiment because the conditions have changed.
Here's why: Collecting the data requires the person with sleep troubles to leave their home environment -- their own bedroom, their own bed, their own sheets. That's not restful. Plus with all those wires and nodes, the sleep subject is bound to be disturbed by being literally tied down. So while the measurements may be precise and exacting, the experiment may not be replicating the same kind of sleep.
The alternative approach in sleep research is called actigraphy, and it pretty much takes the opposite direction. Rather than try to measure every last variable, actigraphy looks to measure just one metric -- movement -- with one sensor (called an accelerometer). What you lose in the details, the theory goes, you more than make up for in the setting. The sleep subject only needs to wear one sensor, usually on their wrist, and they can sleep in their own home, in their own bed.
Research has found that, while polysomnography data corresponds more closely to what actually happens during the night, actigraphy is surprisingly accurate, too. And that the environmental and other factors may more than make up for actigraphy's lack of detailed metrics.
The trade off between polysomnography and actigraphy has been well known among sleep researchers for several years. What's changed in the past couple years is that accelerometers have gotten really, really cheap. Following the familiar trajectory of Moore's Law, the price of accelerometers has dropped from thousands of dollars to hundreds to -- today -- close to $10 a piece. This is why accelerometers are turning up in our shoes, in our cellphones, and in our videogames like Nintendo's Wii. They're incredibly powerful, smart devices that are wonderfully cheap and flexible.
Which brings us to the devices. There are lots of sleep trackers out there, but I've selected five here that seem promising and based in good science. I haven't tested them all myself, so I've provided links to hands-on reviews from other sources. Since the products mostly work with the same hardware, one area to look for distinctions is the software -- the website or app interface. How easy is the device to use and engage with the data it provides? In the end, if you want to start tracking your sleep, you should decide how much infomation you're willing to grapple with (or pore over), and how much you're willing to spend on the experiment.
-Sleeptracker ($149/$179, depending on model): Imagine if your watch told you when to wake up. That's the promise of the Sleeptracker, which looks like a fancy digital watch but, thanks to the accelerometer, sets off an alarm. The approach is simple: You tell it when you want to wake up, and the Sleeptracker goes off when you seem to be in the lightest phase of your sleep cycle. Review by New York Times
-FitBit ($99): The FitBit is an overall tracking tool that puts an accelerometer to work measuring how much you exercise, how many calories you burn and, yes, your sleep quality. I've used one and find it almost imperceptible during the night (it slips into a soft wrist band). Though it's good at gathering the data, though, it's not so clear what you do with it: there's no wake-up function and the data is pretty static on the website. Review by Wired.com
-WakeMate ($49.99): The WakeMate is an effort to streamline the technology every step of the way: the device itself is on a sleek wristcuff, and the tracking tool is in a robust iPhone app as well as website. Like the Sleeptracker, the WakeMate will rouse you in a predetermined window. No reviews; ships 1/25/10. More info from Geek.com
-Zeo ($249/$349): The Zeo calls itself a "personal sleep coach," and it is definitely more involved than the other devices. Indeed, unlike the other devices mentioned here the Zeo DOES use polysomnography, specifically through a headband that measures electrical impulses in the brain. In addition, the Zeo comes with a bedside display that's like a souped-up clock radio; it displays the data as you sleep (which isn't much use) or the next morning. The last part of the Zeo system is the website, where your sleep data can be parsed dozens of ways. The purchase price includes six months of sleep coaching to make the most of your Zeo. Review by Wall Street Journal
-Sleep Cycle ($0.99): This one works with a device you may already own: the iPhone. Using the iPhone's accelerometer, this little app that monitors how much you're moving around. When it detects you're in a light sleep phase around your wake-up time, it starts to play a tune to gently ease you awake. And all your movements are retained as data that you can examine in your iPhone. At 99 cents, it's a great way to sample the sleep tracking concept. Review at 148Apps