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My wife was fine, but her 2005 Honda Pilot was totaled. On Interstate 95 between New Haven and Boston, the SUV had been picked up by the wind from a passing 18-wheeler and hurled against the median strip. My wife told me she wasn’t speeding, but I didn’t really believe her. So I bought a CarChip and (with her permission) installed it in our family’s other SUV, a 1996 Jeep Cherokee. Now I know if she’s been speeding or not–and a whole lot more.

The CarChip is a 35-by-48-by-25-millimeter data recorder that plugs into a connector found under the dashboard of most cars and light trucks sold in the United States and Canada since 1996. The connector lets the CarChip continuously record data, such as speed and acceleration, fed to it by the car’s onboard diagnostics system. To get the data out of the chip, you just unplug it, attach it to a Windows-based computer, and run a downloader program.

The CarChip’s reports contain an incredible amount of data. The report for each trip notes when the engine was started, when it stopped, and how fast the car was going every five seconds in between–all in the form of a pretty graph. The graph is annotated with warning lines that show excessive speed, as determined by the user (my settings are for 70 miles per hour), as well as incidents of sudden braking and acceleration. You can feed the data into a spreadsheet, and if you buy enough chips and special software, you can maintain records for all the cars in your family or corporate fleet.

Davis Instruments makes three versions of the CarChip. The basic chip holds 75 hours of data and costs $139. I bought the CarChip E/X, which holds 300 hours of data, can monitor any 4 of 23 engine parameters (including such geeky things as the oxygen sensor voltage and the engine load), and has an “accident log” that stores the speed of the car for the last 20 seconds before a crash. The E/X costs $179. Finally, for $199, the CarChip E/X with Alarm allows you to set alarms for excessive speed, hard braking, or sudden acceleration. This device is designed to deliver an aud­ible warning when drivers are engaging in risky behavior.

But as any scientist will tell you, it’s one thing to collect data and another thing to understand what the data actually mean. In the case of the CarChip, understanding requires a deep knowledge of the car’s driver and her habits.

One evening two months after I installed the CarChip, I suggested to my wife that we light some candles, put on some soft music, gather at my computer, and review her driving record.

Although the CarChip records only how fast the car is moving, the patterns in my wife’s daily routine made it easy for us to figure out where it had been traveling at which points on the graph. When the car starts at 8:50 a.m., drives three miles, and stops at 9:15 a.m., that’s a pretty good indication that my wife has just taken our twins to school–and gotten there 15 minutes late. She does this with staggering regularity.

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