Chances are, you've probably come to this feature through Facebook, right?
You've also probably noted that Facebook has had numerous pop-ups about their new Terms of Service, which begins from January 1st.
So what's it actually all about?
A privacy lawyer in the UK has had a look through the new TOS (Terms of Service) and reported back.
The new user policy will require people to accept a location data policy, meaning that Facebook will track you using your GPS, WiFi and Bluetooth.
"The idea is to track the location of users in an effort to target them with localized adverts and thus attract more companies to advertise on Facebook at higher rates," explained Maninder Gill, a partner at London law firmSimons Muirhead & Burton.
"The app will help users to find friends who are nearby and alert them when it detects one in close proximity, even when the app is not open on the handset."
Facebook has been at the centre of several privacy scares, most recently relating to Facebook Messenger.
Facebook's Terms of Service are considered by many in the legal profession to be one of the most intrusive.
But what's the likelihood of people dropping Facebook altogether? Unlikely, says Gill.
"Most users will not care and will not quit Facebook and will be too apathetic to bother to go into their privacy settings to recalibrate. And Facebook will just get richer and more powerful."