Katherine Boehret

Let Sleeping Partners Lie

Much less enjoyable than the sound of birds chirping in the morning is the sound of your partner’s alarm clock going off hours before you need to wake up.

This week, I tested the Lark alarm clock and sleep sensor by Lark Technologies Inc., which silently vibrates to wake only the person using it—not both people in bed.

Lark developed the product with a Harvard sleep expert and a sleep coach for pro athletes. The $129 sensor wirelessly connects to an iPhone via Bluetooth and slips into a wristband that is worn while sleeping. The device is available from Lark.com now and will be in Apple stores starting June 14.

In addition to acting as an alarm clock, a sensor on the Lark tracks sleep patterns and measures one’s quality of sleep with Lark Up, a free app from the Apple App Store. All sleep data automatically syncs back to Lark.com, where an in-depth sleep analysis can be found.

There are other devices similar to Lark, like the $60 WakeMate by Perfect Third Inc., which is a wristband that wirelessly connects with apps on Apple’s operating system as well as Android devices and BlackBerrys. A $159 device called Zeo by Zeo Inc. is worn on the head and uses a SecureDigital memory card to transfer data to another device. WakeMate and Zeo are designed to use the data they collect to wake people at the lightest points in their sleep, for a less jarring wake-up.


The Lark sensor and wristband with an iPhone in the charging dock.

A Lark spokeswoman said its tests showed people who hadn’t had enough sleep went right back to sleep when they were woken by alarms earlier than they needed to get up. She also said tests showed users getting mad at their alarms for these earlier wake-ups.

The vibration Lark sends to a person’s wrist is gentle and soothing, unlike the shock of a jolting alarm. The company’s research showed that adrenaline rushes from startling alarms caused people to crash later in the day.

The Lark vibration is slightly different each day so people don’t get used to it and start ignoring it. If you sleep through the vibration, take off the wristband in your sleep or the rechargeable battery dies, the iPhone plays a tune composed especially for Lark. The silent alarm worked like a charm after I strapped it to my fiancé’s arm. I was so undisturbed in the morning, I didn’t notice him getting out of bed. But wearing a wristband to sleep takes getting used to.

For $189, the Lark Pro includes a seven-day sleep assessment and a personal sleep coach aimed at developing better sleep patterns in addition to the wristband and charging dock. Coaching assessments, based on computer algorithms, are approachable and playful: A line from a sample analysis explained why a person woke up so many times in the pre-alarm morning hours by saying “that irritating garbage truck could also be the culprit.”

The sleep coach assigns each person two of 12 sleep types—one based on lifestyle traits (as interpreted from an online survey) and the other on sleep rhythms determined from the Lark data—and offers suggestions and goals for getting better sleep. For example, a Rookie-Erratic is someone who doesn’t get enough sleep and has an unpredictable schedule, prompting the coach to suggest taking power naps and dimming the lights two hours before bed.

At times, the coaching advice seemed to contradict itself. For instance, it told a person to take power naps because of their Rookie side and that same person to rethink daytime naps because of their Erratic side. But an explanation tells the sleeper that naps can be skipped on days when he or she can commit to a consistent sleep schedule and isn’t rushing on deadlines, and that during periods of work marathons, naps are a fail-safe.

Lark still has a few kinks to iron out. At midnight one night, my fiancé accidentally set the alarm for 40 minutes later. He woke up at 12:40 a.m. and then reset the alarm for 6:30 a.m. Though both sleep times and their data were visible on the iPhone, only the data from the 40-minute sleep time was registered at the Lark.com website. Engineers from Lark confirmed this was a bug and said they were reconfiguring the system to transfer the longer sleep time’s data to the website.

The dock charges the sensor and has a USB port for charging the iPhone. A snooze button also works with this product when people tap it on the iPhone screen as their Lark alarm is vibrating. Though Lark is only available on Apple’s operating system for now, CEO and co-founder Julia Hu said Android-compatible Larks should be available by the end of the year.

My fiancé said Lark was less noticeable on his wrist after wearing it the first night, and found that it wasn’t hot to wear—something he worried about. He checked his sleep stats as soon as he turned off the alarm each morning and felt proud when these improved. These include total time asleep, sleep quality (a ranking out of 10), how many minutes it took to fall asleep and how many times he woke up each night.

Like tracking food while dieting, Lark’s sleep tracking statistics give people goals to meet and make them more aware of their behavior and patterns. And even those who don’t care about tracking their sleeping patterns will appreciate the sweet silence and uninterrupted sleep as a result of Lark’s vibrating alarm.

Write to Katherine Boehret at katherine.boehret@wsj.com

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