When the video of the door that unlocks with Foursquare check-ins  went viral, I decided to go see how it works--and whether I could get my own.
It was tempting to whip out my phone, check in and walk right upstairs, announcing that I didn't know where I was--just that I was blindly following my MapQuest. Instead, I fired off a tweet ahead of time and was greeted by Nick Hall , a Brooklyn Web developer at Apartm.net  who happens to have built this little piece of Foursquarey magic right up the street from me in Brooklyn.
Hall and his brother Erin Sparling , also a Web developer, installed the Foursquare door a couple of months ago as a way to let their underlings neighborhood friends and allies enter the office. He took me through the door system and the rest of his uber-wired stuff, which include a home-built touch-screen media system, improvised satellite T1 connection, and a coffee table made of an Apple X-serve.
A Mac Mini chills out near the door and makes requests to Foursquare's API every three seconds, looking for new check-ins at Apartm.net. When the computer finds one, it contacts the Web relay, which sents a simple binary bbzzzz! through a little copper cable that has been soldered to the intercom button in the hallway. The intercom is fooled into thinking the button has been pressed, and it unlocks the door via the building's existing buzzer system. It's shockingly quick. (Right now, only white-listed Foursquare users can get in, but all that will change when the brothers throw their New Year's Party: it'll be open to all.)
Their ISP is a satellite dish aimed at the Empire State Building. See that hole in the wall below? That goes to a satellite dish on the roof of their northside Brooklyn apartment, which is pointed at another dish on the Empire State Building. Using this line-of-sight connection, the brothers were able to get an industrial T1 connection beamed straight to our sleepy Polish neighborhood. Now that better ISPs have arrived, they're transitioning to a hardline connection, but Hall doesn't sound like he's ready to let the satellite go just yet.
They built a homegrown touch-screen media server. Below, you'll see Nick and the office media center to his right. That monitor mounted on the wall? It's a touch-screen that operates the Mac Mini they use as a media server, which you can see on the shelf below the AirPort base station. The touch-screen also powers the projector over the couch, and the stereo. Unfortunately, this system wasn't hooked up, because they're in the middle of upgrading the system to run entirely off an iPad.
Oh, and check out their Nintendo exhibit below the A/V stuff, and the obligatory bucket of bike parts: This is Brooklyn, after all.
This is the coffee table that you do not spill drinks on. It's an X-serve that one of Sparling's students converted into a coffee table for them (he teaches an HTML class, in addition to heading up front-end development for the Wall Street Journal). "Originally, we just put the X-serve here and rested things on it. So we figured we might as well make it a real table," says Hall.
Below, that's a new MacBook Air, for scale (and envy). The Canon 5D on the table isn't the same one they used to shoot the viral video; that's the work of his brother's 5D Mark ii. Oh, and it's worth mentioning that this coffee table is the Web server the brothers use to host the Apartm.net website -- so if this article gets too much traffic, it'll generate a meltown in their living room. (A new HDD is on us, Nick.)
Here's the actual office space where "work," at some point, gets done. The Mac Mini that runs the Foursquare door operation is to the right, outside the frame. Next to it are a few terabytes of backup storage.
Yes, they might sell the Foursquare door system. "We haven't figured out quite how to commercialize it yet," says Hall, but he and his brother are certainly considering putting together a DIY kit. If you think they should, let us know below in the comments, and we'll be sure to follow up with their progress -- we've even been promised Beta tester status. Maybe there's a Kickstarter project waiting in the wings?