With Wednesday’s public launch of iOS 5 — the software that powers iPhone, iPad and iPod touch devices — developers are finding ways to use the latest version of Apple‘s firmware to their advantage. One of the most interesting new aspects of iOS 5 is a feature that allows you to receive a notification when you are close to a specific location.

Foursquare has adopted this to launch a brand new feature called Radar on its iPhone app. The feature allows you to, for instance, receive a notification when you’re close to a restaurant that’s recommended on a list you follow. If you’ve added a venue to your To-Do list, Foursquare will send you a little reminder when you’re nearby, just in case the venue has slipped your mind. Also, if you’re close to a location where a few of your friends have checked-in together, the app will send you a notification so you can meet up with them.

Radar is powered by Foursquare’s Explore algorithm, which means that the feature knows about all the fun, interesting things that are close to your location. Once you’ve turned Radar on, your iPhone will help you discover more fun things to do that you may have otherwise missed. It should be noted that the feature only works on devices running iOS 5.

  

Meanwhile, Foursquare has added a couple of other features into version 4.0 of its app that all users can take advantage of. There are new sharing features and the Me tab has been updated. The location-based service has also made a small tweak to its logo: the ball is now green instead of purple.

Foursquare revealed last month that more than 1 billion check-ins have been made on the service and it added an option to make your home venue more private. The location-based service hit 10 million users back in June, while the launch of Foursquare 4.0 comes 7 months after version 3.0 was rolled out. Foursquare closed a $50 million funding round in June.

You can check out the latest version of Foursquare by downloading it on your iPhone now.