Facebook has been known to be planning some interesting location-based functionality for a while. But the full extent of the plans hadn't been revealed, until now.

Digging through the Javascript on Facebook's "Touch" website shows a function called "Places" that doesn't appear in the live website just yet. Investigating further shows that Facebook is going to launch a version of its website that uses HTML5 to determine your location, and then give you the option to "check in" to local businesses, just like Foursquare and Gowalla.

It doesn't just record your location, it also grabs your altitude, heading and speed - perhaps to prevent some of the cheating that occurs on the aforementioned networks, where people driving along a road can check into all the places along it super-quick. However, for now it looks to only be launching on the mobile version of the website.

We'll bring you more as we hear it.