Because many people check Facebook in the morning and before they go to bed at night, Louv-Jansen was able to piece together information on their sleeping habits (though it only works for frequent users).
Louv-Jansen has published the source code for his tool on GitHub, and explained how it works it in a Medium post last week. Using the software to check Facebook's database on user activity every ten minutes, he created graphics depicting his friends' sleep patterns, and discovered some broad trends, as well. His friends' sleep was largely regular throughout the work week, for example, and more erratic on the weekend.
"MY POINT WAS NOT TO SPY ON MY FRIENDS."
Facebook apparently isn't happy about it. In an interview with The Washington Post, Louv-Jansen said the company asked him to discourage others from using his software, saying that it violates the site's terms of service. (At least 1,000 people have already downloaded the code, he added.) But the developer has refused to remove it from GitHub, saying he created it as a way to raise awareness around how much personal information can be gleaned from freely available information.
"My point was not to spy on my friends," Louv-Jansen tells the Post. "I want people to be aware that they’re leaving some digital footsteps everywhere they go."