If you have a habit of logging into Facebook from your bed, you might be leaving a digital trail that tells people when you're asleep.
The tool collects Facebook Messenger timestamps that show when your friends were last active. It can then approximate how long they sleep each night and when they get up in the morning. Here's what it looks like when the tool shows you this information:
Louv-Jansen explained in a blog post on Medium that he wanted to make a point about privacy and social media.
"In this digital world we leave footprints where we go, and when we do it, without even thinking about it," he wrote.
His sleep-tracker tool relies on the assumption that people who frequently use Facebook check the site before going to sleep and right after they wake up. There's evidence to support this: Studies show that people with smartphones check Facebook 14 times a day on average, and that four out of five of these folks check their phones within a few minutes of waking up.
Louv-Jansen told the Washington Post that the sleep patterns his tool identified were accurate for about 30 percent of his Facebook friends, the ones who used it most frequently. He also found that people's sleep patterns are consistent during the work week, and more random on the weekends.
“I don’t want to say that Facebook is evil," he told the Post. "This is just a side effect of what they’re doing.
Nicole Numrich, a spokeswoman for Facebook Messenger, told The Huffington Post that the company has asked Louv-Jansen to take down his tool.
"Our terms prohibit collecting people's content or information or otherwise accessing Messenger using automated means without our prior permission," Numrich wrote in an email.
So why, exactly, is it creepy that Facebook has a rough idea of when you're asleep or awake?
For one thing, people don't always realize that they're handing over deeply intimate information when they use social media. Every move you make on Facebook creates data that tell the company about your preferences or your lifestyle. The site uses this information to tailor its News Feed to your tastes and show you ads for things it thinks will interest you.
Louv-Jansen's revelation should probably make us rethink our late-night Facebook habits, too. Indeed, young adults who spend a lot of time on social media -- especially those who exhibit "obsessive 'checking' behavior" -- are more likely to suffer sleep disturbances than their peers who don't, according to a 2015 study.
The next time you're in bed and find yourself reaching for your phone for one last scroll through your feed, maybe reach for a book instead.