Foursquare launches version 4.0 with real-time geolocation alerts

Screenshot of Foursquare 4.0 Radar (click to enlarge)

Foursquare on Wednesday launched a new version of its mobile application for the iPhone(s AAPL), Foursquare 4.0.

The biggest change in Foursquare 4.0 is the addition of an opt-in feature called Radar, which is made possible by the latest version of Apple’s iOS mobile operating system, iOS 5.

Radar sends notifications to users based on where they are to remind them to check-in. These alerts are triggered in several ways: when users are close to a place they’ve added to their To-Do list, when they’re close to a place that’s on a Foursquare list they follow, or when three or more friends are checked into a nearby venue. The Radar feature works whether the Foursquare app is open or not, the company said in a blog post.

Radar is an interesting extension of Foursquare’s lists feature, which made its debut in August. Now that the app knows about places a user hopes to visit, vs only knowing about places she’s visited in the past, a feature like Radar can be useful instead of annoying. In all, it seems like a smart evolution for Foursquare, which has been on a growth and R&D tear since it secured $50 million in new venture capital in June.