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GSM, black boxes, and iPhones: the tech that drives Zipcar

Zipcar is more than a simple car sharing service—it's a technological …

Those living in urban environments probably know all about car-sharing service Zipcar. For the rest of the world, Zipcar made its global splash by demoing its upcoming iPhone app during the keynote at this year's Worldwide Developers Conference in San Francisco.

The impressive demo not only stood out to numerous iPhone-owning Zipcar customers—it generated a flurry of curiosity among the geek crowd about what Zipcar is and how the technology behind the service works. After entertaining a few discussions here at the Orbiting HQ as well as numerous reader questions, we decided to take a peek behind the curtain at Zipcar to learn more about the system, learning that it's more complex—and cooler—than we originally thought.

What is Zipcar?

For those who aren't yet familiar with Zipcar, it's a car sharing service located in more than 50 cities across the US, Canada, and UK including (but not limited to) Chicago, New York, San Francisco, Phoenix, Boston, Seattle, Milwaukee, Nashville, Atlanta, London, and Toronto. Think of it like a rental car service that lets you rent cars of all types by the hour. It's geared towards people who don't own a car (either by choice or necessity) but still need one on occasion for errands, trips to see the parents, road trips, or whatever else.

For between about $7 and $12 per hour—depending on the car—Zipcar covers gas, insurance, parking, and most mileage. All you have to worry about is a yearly membership fee of around $75 and showing up to take the car for a spin. I've been a Zipcar user (or, as Zipcar likes to call us, a "Zipster") for more than two years now and have saved thousands of dollars just on insurance and maintenance alone since selling my 2004 VW Passat. It's also incredibly helpful for running errands when I'm traveling for work, as I can grab a car as quickly in San Francisco as I could at home—no annoying rental car offices or paperwork required.

From the customer's perspective, it works like this: I make a reservation via the Internet or phone (I obviously prefer Internet, either on my computer or through the mobile website). I can make reservations weeks in advance or right this very minute, depending on which cars are available. The site will show me the cars that are currently open and where I can find them—where I live currently, there are tons to choose from within just a couple blocks, from BMW Minis, to Mazda 3s, to Volvo S40s, to Toyota pickup trucks and everything in between.


After making the reservation, I walk to the car of my choosing and wave my Zipcard over a sensor on the windshield. The car unlocks and I grab the key, which is attached to the dashboard, and off I go. When I return the car, I wave my card again and the car locks. The company bills the reservation straight to the credit card I have on file.

The tech behind it

I spoke to Zipcar CTO Luke Schneider to learn more about the inner workings of this system—how does the car know I'm the right person showing up at the right time? Schneider explained that it requires a mix of wireless and hardware technologies to function. All cars are equipped with a "black box" of sorts—Zipcar's own design—that connects to three major systems in the car: the ignition, the lock circuit, and serial data that comes from various sources within the vehicle. The black box also contains a wireless modem that communicates over the GSM network (actually, GPRS—the old, slow cell data protocol that predates 3G and EDGE).

When a reservation is made on the Internet, a package is sent over GSM to the chosen car and stored in a ring buffer until the driver shows up with his or her Zipcard, which is equipped with an RFID chip. The cardreader mounted in the windshield reads the RFID signature to authenticate the holder of the card and sends the message to the computer in the car. From there, the computer asks itself three questions: Am I the right car? Is it the right time? Is this the right driver?

If all of the answers are in the affirmative, the car unlocks and the driver gets in. At that time, an immobilizer is also released so that the engine can start. Without this authentication step, the ignition cannot work—"If somebody smashes a window and tries to take the car, they can't, because the mobilizer circuit wouldn't be on," Schneider explained. (Good to know.)

Where the iPhone app comes in


The iPhone app demoed at WWDC basically combines the mobile version of the Zipcar website with the Zipcard functionality. Not only does it allow users to search nearby (or anywhere) to find cars, they can also read details about the cars, make reservations, see maps, and, once a reservation is made, unlock the car directly from the phone. And, for those who lose their cars in parking lots easily (*cough*), users can even make the car honk remotely.


The app has yet to become available, and Schneider would not tell me when we could get our hands on it. "Soon!" he insisted. "The reality is that the app is in pretty good shape, but there are a number of things that are outside of our control to determine the exact release date." Translation: it's stuck in an Apple approval holding pattern for who knows how long.

But pretend for a moment that the iPhone app exists and that people can use it. "The iPhone is really a surrogate for the Zipcard," Schneider said, explaining that it sends the same signals to the car to unlock it as the Zipcard would, except from the phone instead. "Depending on where the car is, we leverage two different technologies. One is short-range wireless and the other is the GSM network like the Zipcard would." Schneider declined to elaborate on the "short-range wireless" part of the equation as it's apparently proprietary technology, though he summed up the experience as "virtual remote keyless entry" (imagine the remote key fob that comes with most modern cars and put it into software form that communicates over GSM).

Are other smartphones going to get any love?

This led us to our next question: why the iPhone, and when are other smartphones going to get in on the action?

"The iPhone was a natural idea that flowed out of some research we had done earlier in the year," Schneider explained. "Fifty-five percent of our members own a smartphone, and half of those smartphone users had iPhones. As a consumer brand, it was a clear and logical decision to go with the iPhone first." 

He then went on to say that the company is definitely looking at other mobile platforms, but it depends on where the Zipcar membership is going. "If what they're telling us is that the BlackBerry is the most important, then we'll listen just like we did before," Schneider said.

Schneider believes that part of the Zipcar philosophy is simplicity, and the company is constantly working towards removing any discontinuities in the experience (such as searching for your Zipcard when you already have your phone on you). "It's all about mobile right now," Schneider said. He hinted that there was much more to come—"additional functionality like location-based services and cloud computing"—but declined to give away the goods for the time being. Wait—cloud computing? Schneider reassured me with a cryptic closing message: "No matter what we do, members always benefit."

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