“Perhaps these are useful for estimating sleep time, but their usefulness in estimating sleep stages is probably limited,” Scharf says. Here are three:
The Sleeptracker watch is a “sleep phase monitor and vibrating alarm [that] gently wakes you at the most optimal time.” You enter an alarm time, plus how much earlier than that time you’d be willing to wake up, from not at all to 90 minutes. The watch will vibrate and/or beep sometime during that time window when your sleep cycle is in an “optimal, almost-awake moment.”
Once you’re up, you can plug the Sleeptracker into a computer to download a graph of your “almost-awake moments.” (Scharf says about 30 such episodes a night is normal.) The software shows the average time between these episodes. You can check off factors that may have affected sleep, such as alcohol, noise and late-night snacking, to determine which factors might be interrupting your sleep. Associating stillness with “deep” sleep and wiggling with “light” sleep is an oversimplification at best and not accurate at worst, Scharf says. For example, slow wave or “delta” sleep is a deep, restorative stage and we can and do make movements during it.
(99 cents, www.mdlabs.se/sleepcycle)
This app is much less expensive than the other gadgets, but it’s compatible only with the iPhone or iPod Touch. Sleep Cycle uses those devices’ built-in accelerometers — it’s the technology that allows people to use their iPhones as steering wheels or light sabers in games — to track motion during the night. The user is instructed to leave the iPhone or iPod on the corner of the mattress, near the pillow. (People who feel uncomfortable having the iPhone emitting its small dose of radiation next to their heads all night may set the phone to flight mode.)
Like the Sleeptracker, Sleep Cycle claims to wake people at an optimal phase of sleep within a preselected wake-up window. The “intelligent snooze” feature lets the sleeper snooze for shorter and shorter periods until the alarm time.
Fitbit Wireless Personal Trainer
Fitbit is a “24/7 health and wellness monitor,” according to a company spokeswoman, so it tracks sleep as well as activity throughout the day. For sleep tracking, you can wear the Fitbit on your wrist at night. In addition to an accelerometer, the Fitbit uses a 3-D motion sensor, similar to the one in a Nintendo Wii, to capture movement. The creators say the device can tell how long it took you to fall asleep and how many times you woke up. Based on that data, which is wirelessly uploaded online, it assigns a “sleep efficiency score.”