Device Tracks How You're Sleeping

A new system monitors your sleep patterns at home. But will it improve your sleep?

If you had asked me this morning how many times I woke up last night, I would have guessed four or five. But according to the Zeo, a new gadget that monitors a person's sleep, it was a disturbing 15 times. I'm also getting considerably less sleep than I thought, averaging about six to seven hours rather than the seven to eight hours I had always estimated.

Sleeping soundly? Novel sensor technology embedded in a soft headband (shown here) allows a new sleep-tracking device, called the Zeo, to determine a user’s sleep state. The data is sent wirelessly to a bedside display unit, also shown here, which shows the user’s sleep patterns. Credit: Conrad Warre/Technology Review

The Zeo Personal Sleep Coach, developed by a startup headquartered in Newton, MA, is the first at-home device that allows people to track their sleep cycles over time. With a simple headband recording system, the device represents a neat feat of engineering. And it certainly seems to tap into an interest--everyone I told about the Zeo wanted to test it out, a testament to our obsession with sleep, or lack thereof. It's not yet clear that it will truly help users improve their sleep, but it may present a new opportunity in sleep research, allowing scientists to track normal variability in sleep much more cheaply and on a broader scale than before.

In essence, the Zeo is a highly simplified and automated version of the technology used to assess patients in sleep labs. (The company is careful to point out, however, that the Zeo is not a medical device and cannot diagnose sleep disorders.) While sleeping, users wear a sensor-laden headband that measures electrical activity in the brain. That data is wirelessly transmitted to a display unit like an alarm clock that sits next to the bed. In the morning, the display unit gives a summary of the previous night's sleep, including how long a user slept, how many times she woke up, and the amount of time she spent in the various stages of sleep. A small memory card within the display unit stores the data, which can then be transferred to a computer and uploaded to a website that tracks the user's sleep trends and offers advice for improving sleep.

"I see it more like an assessment, such as a blood-pressure monitor or weight scale, to monitor your physiology," says Phyllis Zee, a sleep scientist at Northwestern University in Chicago, who is also a scientific advisor to the company. "Sleep is really the next vital sign."

A growing pile of research emphasizes the crucial importance of sleep, linking it to everything from memory to obesity. A typical night's sleep involves a repetitive cycle of light sleep followed by deep- or slow-wave sleep followed by REM (rapid eye movement) sleep--the time when we dream. These phases keep repeating, with the duration of each cycle shortening as the night progresses. "The duration of these cycles and the number of cycles are indications of sleep quality," says Michael Twery, director of the National Center on Sleep Disorders Research, part of the National Institutes of Health in Bethesda, MD.

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While the company won't divulge specific details on its technology, the biggest innovation lies in the Zeo's sensor and the algorithm used to process the information it records. In sleep labs, brain-wave activity is recorded via a number of electrodes attached to the scalp, a technique known as electroencephalography (EEG). Because this approach is highly susceptible to noise, the electrodes are placed in precise spots for optimal recording, and a conducting gel is usually smeared between the electrodes and the skin to improve the signal. Researchers at Zeo have developed a novel technology using dry, silver-coated fabric electrodes that sit on the forehead (typically not considered a great spot for recording EEG activity).

An algorithm that was developed using neural-network analysis processes the messy electrical information recorded by the sensor and automatically determines the wearer's stage of sleep. (In a sleep lab, a technician watches the activity in real time, regularly scoring the patient's stage of sleep.) "The algorithm is designed to mimic what an expert sleep scorer would report," says John Shambroom, Zeo's vice president of research. A comparison of the Zeo to traditional, technician-scored polysomnography--EEG and other measures used in a sleep lab--found that both performed similarly in healthy people, he says.