Sharing your location on social media can sometimes be helpful. For example, when I was a college student I would check-in to the library on Foursquare before sitting down to study. Throughout the night of homework, I would be joined by friends and classmates I had allowed to see my Foursquare check-ins, and studying became a little less awful. It was really great if one of my Foursquare friends ended up helping me study or proofreading an essay. I liked knowing that my friends knew where I was.

But then there’s the other side of the coin: when everyone else knows where you are. You don’t know these people; you can’t trust them. There are a few “public service announcement”-style websites to show you how creepy that can be, and a new one just popped up. WeKnowYourHouse.com launched on Sunday to raise awareness to the fact that checking-in is telling the world where you are. The website creators say it is a “social networking privacy experiment that has been designed to show what could happen when you tweet about being at home with locations enabled, particularly from a mobile device.”

The data is collected through the Twitter Search API, and pulls tweets talking about ‘home’ with a location attached. The location may be from tweeting a check-in, but it could also be from sending any tweet if your Twitter account settings have allowed Twitter to geotag your tweets. WeKnowYourHouse.com pulls tweets containing phrases like “at home” with location data attached and uses the Google Street View web API to post a possible picture of the home.

The website isn’t designed to compromise your safety. The creators say that they only store the most recent data, and posts are deleted after an hour on the site. There is also an opt-out option. But they want to wake you up: if they can find all of this information about your whereabouts, so can anyone else.

When the website first launched on Sunday, the site showed even more information than it does now. It initially showed the tweeter’s full Twitter handle and left the street address visible. After their Twitter account was suspended, the creators made a few changes and relaunched yesterday. Now, the Twitter handles and addresses are partially censored, but anyone could head straight to the search bar on Twitter.com and find the tweet through a quick Twitter search.

Other people have also taken it upon themselves to teach people about being careful on social media: PleaseRobMe.com started in 2010, which is sort of the opposite of WeKnowYourHouse.com. It lets you enter a Twitter handle and displays shared check-ins from Foursquare or Gowalla to show you that by tweeting that you’re not at home, you’re practically asking burglars to break into your house. Then there’s the @NeedADebitCard Twitter account, which retweets photos people have shared of  their debit and credit cards with the numbers visible. The account’s Twitter bio says it all: “Please quit posting pictures of your debit cards, people.”

We’re not discounting location-aware apps completely, because they can be great. But using apps like Foursquare and Path requires the user to be aware of the implications of sharing their location. Here are some precautions you can take:

• Choose your friends and privacy settings carefully. This is wise for any social network, but especially ones that know your location. Keep your friends list short and make sure you know and trust everyone on it.
• Don’t share geotagged posts such as check-ins on Foursquare and Path to more public social networks like Facebook or Twitter, especially if those accounts are public or you have a large number of friends or followers.
• Double and triple check your account settings on all social networks that have geotagging options, especially on mobile devices.
• Do not check-in to your home. Instead, you can choose to check-in to your housing complex, neighborhood, or city.

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