How to buy police license plate readers

By Tim Dees

While privacy advocates condemn Automatic License Plate Recognition Readers (ALPR) systems as an intrusion into their right to move about freely and unmonitored, the cops using them are ecstatic, and their reasons have nothing to do with privacy concerns. ALPR is a force multiplier.

One officer with a mobile ALPR system may recover more stolen cars and locate more vehicles associated with wanted persons and scofflaws in a week than another would in a career. Here's a few things to consider when purchasing ALPR tech:

How they work
There are stationary and portable or hard mounted mobile ALPR installations, but they work the same way. One or more cameras scan license plates as they come into view. Using software monitoring, the camera output isolates the characters on the license, translates them from graphics into letters and numbers, and compares the string of text against an internal list of license numbers of interest.

When it finds a match, the operator gets an audible alert, with his computer display showing an image of the whole car, the license plate, the machine's translation of that plate, and the reason the plate is on the list. The officer verifies the plate matches the one on the list, and decides whether to chase it down, direct another unit to do so, or just log the sighting. A passive, usually stationary system records all this for later review.

There's too much data to "run" each plate in real time, so only the internal list is used for comparison. That list can contain stolen vehicles or vehicles associated with wanted persons, those having expired or suspended licenses, those not carrying insurance, or cars with too many unpaid traffic tickets. Most users update the list daily and transfer it via a USB thumb drive.

Mobile systems
Mobile systems mount on most patrol cars, with cameras on the light bar or the bumper. Some provide for switching the cameras from one mount to the other. The operator points the cameras fore and aft or laterally, depending on whether he's monitoring cars passing on a highway or driving through a parking lot. Some systems with high resolutions cameras offer the capability, without camera adjustments, to read cars passing on the highway or cars parked on the street and in a parking lot.

In-vehicle software
In-vehicle software is usually designed to be very user friendly and touch-screen enabled. The operator has to be able to use the equipment and still drive the car without undue distraction. Most systems will run on notebook computers already installed in your cars.

"Back office" software
"Back office" software is the system running in the station that compiles the lists of license plates from whatever sources you choose, maintains a database of scanned plates and images, and purges the scanned data on whatever schedule you select. Insist on a real-life demonstration of these capabilities before you sign off.

These systems are expensive, at $20K-$30K or more per vehicle. Because they do so well at locating stolen cars, some insurance organizations will assist with purchase.

Tim Dees is a retired police officer and the former editor of two major law enforcement websites who writes and consults on technology applications in criminal justice. He can be reached at

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