Imagine you are at a restaurant with 20 people, both family members and friends. You pull out your smartphone and tell everybody that you quickly have to check-in. How many of the people around you would understand what it is that you are doing?

As we have written about before, the check-in has become the default way for people using mobile services such as foursquare, Gowalla, Brightkite or Loopt to tell the world where they are. Instead of the mobile phone monitoring their location automatically and publishing their whereabouts, users actively press the check-in button when they feel comfortable revealing their location.

But so far, these kind of location based apps have solely been an Early Adopter phenomenon, reaching only a few million people around the world (foursquare has less than 3 million users, Gowalla doesn’t even have 500.000 yet). Hence, the majority of people won’t associate the check-in term with web apps but rather with airports where checking in means leaving your luggage and getting your boarding pass.

Do the test: Ask your family, friends and colleagues what a check-in is. And then wait a year and do it again. You can be sure that the result will be significantly different. Why? Because Facebook, the world’s biggest social network with more than 500 million active users has recently launched a check-in feature called Facebook Places. At the end of last week the site started to roll-out the feature to users in the US, but we don’t expect it to take more than a few weeks or month to see the Places feature launching globally.

With Places, Facebook has finally done what many observers of the Internet for a long time have expected to happen: It has launched its own location service based around a check-in functionality. The feature works exactly as you would imagine: Depending on your coordinates you get a list of locations around you where you can check-in, or if the location does not exist yet you can add it. Every location has its own profile page which shows recent check-ins of other people.

Additionally, Facebook gives you an overview about where you friends are at the moment, making it much easier to meet up with some of your contacts who might be close to your current location.

By betting on the location trend, Facebook is bringing the concept of checking in and seeing where your friends are to the mainstream. So far, the biggest problem with the smaller services mentioned above is that not many people do use them, and for most users I know, the foursquare and Gowalla friends mainly consist of their Twitter peers, who not necessarily are their close friends. In fact, only very few of my “real” friends are using location based services, which means that I hardly benefit from the capabilities location based apps do offer in theory.

But I expect this to change, since almost all of my friends are on Facebook, and lots of them do own a smartphone. After having launched Places on a global scale, it won’t take too long until many of your closer friends will have tried the new feature, giving everyone new insights about favourite places and interesting locations. And since Facebook is providing existing location apps with a new API to integrate their functionality with Facebook Places, loyal foursquare or Gowalla users can continue to check-in with those services and will see their Facebook friends’ check-ins as well.

It’s for sure that Facebook embracing the check-in concept won’t be the final evolution step of location based services (background monitoring and automatic check-ins at favourite locations using Geofencing will become common in the future). But the move means that the whole idea of telling other’s where you are by using your mobile phone is brought to the masses, and the check-in as term will become as common as other expressions introduced by web services such as “to google” (which in several European languages is synonymously used for doing a web search) or “to poke”.

While we at Twingly can’t wait to try the new Facebook Places feature, it will be interesting to see how Facebook handles the inevitable privacy-related user backclash. While the possibility of telling all your friends where you for some users is reason enough to be concerned, Facebook didn’t make it easier for them by adding a potentially questionable feature which lets you check-in your Facebook friends (it’s required though that you have checked in at the same location). It’s possible to deactivate this feature but in best Facebook tradition the site made this process more complicated than necessary.

We’ll see if the feature will be abused by some who find it funny to check-in at some dubious location just to be able to tag their friends as well. It’s not impossible that Facebook might do some fine-tuning with Places before rolling it out globally. But in any case it’s only a matter of time until even your grandparents will understand what you mean when you tell them that you have to check-in.

/Martin Weigert