"By creating a simple service that checks Facebook every 10 minutes, I’m able to get an accurate picture of my friends’ Facebook usage," he said in the blog post. "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)." However, the tool is less effective when attempting to track the sleeping habits of people who aren't very active.
To demonstrate, Louv-Jansen used the tool to generate graphics showing his friends' sleep patterns, and even noticed trends like their erratic sleep habits on the weekends. In addition to explaining the creepy hack, he published the source code for the tool on GitHub. Facebook, however, is not pleased and warned using his tool is a violation of its terms of service, according to a report by The Washington Post.