Developer Says You can Track Your Friends' Sleep Habits Via Facebook

This tool (most likely) knows when the most frequent Facebook users sleep.

— -- The digital bread crumbs users leave behind on Facebook can be used to piece together an eerily accurate profile of your friends' sleeping habits, according to a Danish software developer.

Facebook's Messenger service, an app that provides text and voice communication, shows when a friend was last active. That developer, Søren Louv-Jansen, a Danish software developer who isn't affiliated with the social network, said he found a list of users IDs and last activity on, the web-based version of the app.

In a blog post on Medium, Louv-Jansen explained how he then created a source code that checks Facebook every ten minutes to get a picture of who is and isn't active. For the most frequent Facebook users on a friend's list, that data can then be mapped to show when your friends use Facebook.

"Many people visit Facebook as the first thing in the morning, and the last thing before going to bed. It is therefore possible to get a good impression of their sleeping habits (or lack thereof)," Louv-Jansen wrote.

He linked to the source code in his blog post, making it available for anyone to try. Louv-Jansen said he created the code because he wanted to show that "we cannot hide."

"Everybody I’ve shown this to (has) been equally fascinated and outraged by the accuracy with which it predicts their sleep habits," he said. "In this digital world we leave footprints where we go, and when we do it, without even thinking about it."

Facebook told ABC News in a statement "our terms prohibit collecting people's content or information or otherwise accessing Messenger using automated means without our prior permission."

"This integration violates those terms - as the developer alluded to in his post - and we've reached out to the developer to ask him to take it down," the statement said. "Messenger cares deeply about protecting people's privacy. That's why only people you're Facebook friends with, have added as a Messenger contact or who you've messaged before can see when you were last active."