mobilesecurity.com [Mountain View, CA] For one glorious day, I was the mayor of San Jose International Airport (SJC). But the very next day, I was ousted. There wasn’t a lot of pomp and ceremony. It wasn’t like the Lord Mayor’s Parade in London, and I’m no Clint Eastwood. It was a quiet affair, just me, my baggage, and the rental car station.

So what exactly am I talking about? I’m an avid user of Foursquare, the location-based social network that now has 20 million users checking in 3 million times every day. With Foursquare on my mobile device, I can “check-in” and make my presence known wherever I am, and I can make this check-in private or I can share it with my Foursquare friends. I can be even more public by publishing it on my Twitter stream or Facebook feed. To become mayor of a location that I need to have more check-ins than anyone else in the previous 60 days – and everyone who subsequentyly checks in to the same venue will know my name. Unfortunately it doesn’t come with a cat skin windcheater or treasures beyond my wildest dreams, but we can’t have everything

Who cares? Social media oversharers like me care a ton. Enough people care about sharing their location, that Facebook introduced a feature called Nearby (initially called Places). People check-in for the same reason people post photos and status updates: they want to be heard and seen and they want to show people what they eat, where they’ve been, who they’ve been there with and what they’re doing while they’re there.

With all this sharing comes a loss of of privacy. When you check into places— on Foursquare, Facebook or any other check-in service, unless you’re very careful with your privacy settings and behavior, you could be telling people more than you intend to share. Posting on Foursquare and Facebook tells people exactly where you are at any time. It tells people you’re not home, and just how far you are from home. There are services available that track and display Foursquare logins over time so people can start noticing your travel patterns. If you check-in everywhere including your gas station and grocery store, the vicinity where you live becomes evident. If you check in at home, who knows who might know.

This doesn’t mean that nobody should use location services. Most of these are very useful. Google maps needs to know where you are to help you with driving directions. Yelp needs location services to know where to suggest that has great food around you. Weather apps need the location to tell you the 5-day forecast. For apps in general though, be cautious when the app asks for your current location. Understand what the app is going to be using your location for, and then decided whether it makes sense or not. Understand how to turn this permission off when it isn’t needed.

If you simply can’t help yourself, and insist on sharing your location by checking in absolutely everywhere, do some things to limit the risk of compromising your personal privacy. Keep your network as private and as locked-down as possible. Do not check in at home or close to home too often. If you must check in to a hot new restaurant you scored reservations for, wait until you’re about to leave instead of as soon as you arrive. 

You can never be too careful. I’m an avid cyclist and I enjoy using MapMyRide which uses your GPS to track and record your rides from start to stop. You can save them and share them. If you’re not careful, you could be revealing your home location. I always start the app recording about a mile away from home to keep it private. If you don’t want to go that far, simply don’t share them on a social network.

Location-based services are very popular and normally very useful. While most apps and services are totally harmless, good sense and a few simple steps will keep you and your privacy safe.