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In writing my weekly real estate feature Block x Block, I often need to track down the history of an old building. It’s useful information for potential tenants, buyers, even casual tourists or passersby. To get this information I typically have to track down a local historian or look up the building on the historic registry (that is, if it’s listed there). But I found a group of buildings in Chicago whose histories are instantly available to anyone with a smartphone.

As , a new app by the Society of Architectural Historians will send a building’s history to your phone when you take a picture of the building’s “barcode” on a sign in its lobby. I put “barcode” in quotes because it’s not really a barcode – it’s a little image – but it works the same way.

Here’s a map of the buildings and some instructions. The little boxes are the images you photograph to get the building’s history.

The app, called the 2010 SAH Annual Meeting Chicago Loop Walking Tour, is a Microsoft app and is available .

If this idea spreads, it would make my job easier. Maybe your job, too.