Worried that a high-tech in-car black box might rat you out to the law? Civil libertarians fret that your car might be forced to bear witness against you after an accident, or possibly even when you're pulled over for speeding. If it's any consolation, police officers in Altamonte Springs, Florida, are in the same boat... well, car.

The Altamonte Springs PD was averaging five to seven instances of phantom vehicle damage each month, meaning damage that averaged $1,800 in repairs showed up without any of the Central Florida city's 102 officers reporting or at knowing about it. Frustrated, the town fathers ordered and publicized the trial installation of 30 vehicle data recorders. The recorders are essentially accelerometers with time and date stamping that record the magnitude and direction of sudden acceleration. Which really means sudden deceleration, if say a fast reversing car smashes into a fire hydrant. According to the Independent Witness of Salt Lake City, in the following six months, the number of "unallocated property damage" events dropped from a half-dozen per month to one in six month. The city then equipped the rest of the fleet with the devices.

You may actually be driving a car with a black box right now and not know it. More than 20 million cars have data recorders now, including all GM cars manufactured since 2004. Because of the hassles involved in getting a search warrant and finding compatible equipment to download the data, it's not likely police are going to try to grab readouts just to substantiate speeding tickets. But in serious accidents, it might help determine what really happened – not just speed, but also the force of the impact.

Data recorder/accelerometers are heavily used on commercial trucks, on cargo containers, and even within valuable but delicate devices that are being shipped. Some data recorders can wirelessly report their position in case of theft, as well as determine when a shipment was jolted or damaged, which is especially useful when several carriers handle a shipment and no one accepts responsibility for the damage.