Foursquare has just released a major update to its iOS app for the popular location-based social network introducing a new iOS 5 feature, foursquare Radar. Designed to work in tandem with the enhanced location features of iOS 5, foursquare Radar allows users to receive notifications about interesting and cool things happening nearby. The features leverages information in the user’s Foursquare profile such as lists they’re following, to-do items they’ve created and friend relationships to provide notification alerts when things are happening in the user’s current vicinity. For example, Foursquare can notify the user when they’re near a venue that is on a followed list or to-do item or when a group of friends are meeting up nearby. Once enabled, notifications occur whether the app is running or not and appear in the iOS 5 Notification Center. Foursquare 4.0 remains compatible with iOS 4 and provides some new sharing features and an updated ‘Me’ tab as well, however the Radar feature requires iOS 5 and an iPhone 4 or 4S—as with the built-in Reminders app, location notification features are not available on the iPhone 3GS due to the lack of region monitoring support in the hardware. Foursquare 4.0 is available from the App Store as a free download.