A developer had an idea to see how one might use Facebook to see when friends are awake. Søren Louv-Jansen discussed his thoughts and technique on Medium. "Like most of my friends, I use Facebook on a daily level," he wrote. By using Facebook, that meant the website, Facebook app, and the Messenger app.
Louv-Jansen had his own message: "It should come as no surprise, that Facebook keeps track of every time you visit them through any of those means. The creepy thing is, that your friends can keep track of this too."
Facebook launched messenger.com — a web-based version of their Messenger app. In the web-based Messenger, he explained, and it is possible to see when a user was last active. He found a list of user ids and timestamps of last activity. "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). "
He got creative. He came up with a simple service that checks Facebook every 10 minutes, and he was able to get an accurate picture of his friends' Facebook usage. The 'time stamps' from Facebook's own Messenger service gave him an idea of friends' sleeping habits.
Matt McFarland in The Washington Post described how this works: "Facebook stores timestamps on when its users were last active on Facebook and its Messenger service. Louv-Jansen's tool automatically collects this information to create visual depictions of his friends' sleeping habits. He said it worked extremely well on 30 percent of his friends, and somewhat effectively on the remaining 70 percent. He learned that sleep patterns are consistent Monday through Friday but random on the weekends."
McFarland also raised a point about all this: "If you're a devoted Facebook user, it's alarmingly easy to tell when you sleep. The service is not as effective at tracking less regular users of Facebook."
Louv-Jansen published the source code for the service that can check out sleeping patterns of friends on GitHub.
Moral of the story, he said in Medium, was that we cannot hide. In this digital world we leave footprints where we go, and when we do it, without even thinking about it.
Also, he stated that his motive as not to offer a neat way to spy on people, according to The Washington Post. He further explained, "I want people to be aware that they're leaving some digital footsteps everywhere they go."
As such, he said he had no desire to say that Facebook is evil. "This is just a side effect of what they're doing." Nonetheless, he heard from Facebook and the message did not say Congratulations.
From The Washington Post: "The Dane said he heard from Facebook on Tuesday that use of his program violated the social network's terms of service. He said he was asked to discourage others from using it. Louv-Jansen said he has already stopped using the tool himself. But he refuses to remove it from Github, where he published it."
Louv-Jansen's GitHub page carries this disclaimer: "Facebook reached out to me and informed me, that it is against their terms to access their website by automated means. Additionally I am not allowed to urge anyone to do so. Therefore: I urge you to use this project for educational purpose only, and not use it to access Facebook."