Former Baltimore police officer Bob Kleebauer conducted his own road test. Late one night in March, he drove to the intersection where his wife got a photo-radar ticket. His license plate coated with PhotoBlocker, he waited until no cars were coming, then ran the light.

He took that "$75 chance" because he believes red-light cameras are
revenue traps targeting decent people, says Kleebauer, now a telecom
salesman. "Ninety-nine percent of the drivers who get caught are
law-abiding citizens who do it accidentally. You are approaching a
yellow light and you have a tenth of a second to brake or go. Make
the wrong decision and they got you."

His test finding: "The flash went off behind me, but I've never
received a ticket."

The Denver Police Department, at the behest of Fox News, conducted a
road test two years ago and found that PhotoBlocker was effective,
plate covers less so. Similar results were found by TV news programs
in Great Britain, Australia and Sweden.

[...]

Ray "Radar Ray" Reyer, whose online firm Radarbuster.com sells Photo Fog and PhotoStopper, says roadside and weather conditions and camera angles can affect clarity. And the "flash-back" sprays have no effect against digital cameras that don't flash, like the ones Howard County recently began installing.

[...]

Speed Measurement Laboratories -- consultants to police departments
and radar and radar-detector makers worldwide -- has tested most
products designed to defeat photo enforcement, including car waxes
and stealth sprays that claim to make cars "invisible to radar,"
photo-flash devices designed to flash back at cameras and the
high-gloss tag sprays.

"There's a lot of good people in the industry who are honest and a
lot of charlatans. But it doesn't work, that's the bottom line,"
says Carl Fors, owner of the Fort Worth company.

The bounce-back-the-flash concept does work sometimes, he says, but
only on positive images traffic cameras produce. "If we reverse the
image, go to a negative image, we can read every letter on a license
plate," he says.

Fors says the firms that make and operate radar camera systems and
analyze the photos for municipalities routinely check negatives
where license plates look unreadable. "Going to the negative image
is no big deal," he says.