Having been rumoured for months Facebook has finally unveiled its geolocation check-in service Facebook Place. That’s right it has a check-in service just like Foursquare. Is it a killer? Or will its presence act as a conduit to help massively expand the nascent sector?

Like Foursquare, which was  present at the launch along with other mobile “partners, Facebook Places will allow users to share their location by “checking in” to a place, letting friends know where they are, and see if any of their friends have also chosen to check in nearby.

First up this is initially only available in the US, but Facebook says it hopes to roll it out in other countries pretty soon. I know you’re desperate to check-in.

Platform wise the launch is also pretty limited. It is only available to those who have the most recent version of the Facebook app for Apple’s iPhone or via the touch.facebook.com site using a mobile browser that supports HTML 5 and geolocation.

Once the Facebook Places app is up and running on your iPhone you tap the “Check In” button to see a list of places nearby. It is a case of simply choosing the place that matches where you are or if it’s not on the list searching for it or add it.

The act of checking in creates a story in your friends’ News Feeds and will show up in the Recent Activity section on the page for that place.

What it also does is when you check-in it allows you to say who you’re with and tag your friends in the same way you can tag a friend in a status update or photo. So you have multiple group check-ins.

The app allows you to see others who are checked in with you at that place in the “People Here Now” section.

In a nod to some of the privacy issues that Facebook is bound to face with Places the “People Here Now” section is visible for a limited amount of time and only to people who are checked in there.  If you prefer not to appear in this section, you can control whether you show up by changing your privacy settings.

There is quite a strong focus on privacy around the Places launch. Clearly Facebook recognises that its new service opens up a new series of privacy challenges.

Michael Sharon, Facebook product manager for Places, says: “You are in control of what you share and the people you share with. You choose whether or not to share your location when you check in at a place. When you check in, you can tag friends who are with you but only if their settings allow it. When you are tagged, you are always notified.

“Only your friends can see when you visit or are tagged at a place, unless you have specifically set your master privacy control to ‘Everyone’.” You also have the choice to set more restrictive customized settings.”

The mobile partners/rivals

There has been a lot of discussion about what the launch of Facebook Places means for the competition, which makes it all the more interesting to know that Foursquare, Gowalla, Yelp and Booya were all at the launch. Everybody is “happy” to be working with Facebook, but how happy is a good question.

Just how many check-in services do you need? Foursquare might have been at the Places launch talking about its platform, badges and gaming and reward elements (points of differentiation), but Facebook Places is clearly a threat to its future. No doubt about it.

By the same token Facebook’s entry into the geolocation market could also open it up and bring check-ins to the masses. It could prove a major shot in the arm to something that is still very niche when it comes to widespread adoption.

Other stuff – what your friends can do for your

Your friends can also check you in. When a friend tags you through Places, you get a notification on your mobile and the first time this happens you will have the choice to allow your friends to check you in to places.

When they do this it is the same as check-in in yourself and likewise you also will appear checked-in to your friends.

If you choose not to allow friends to check you in then when they tag you at a place, your name will appear in the same way it appears in a tagged status update – just without appearing checked-in.