In the medical world, it's called a placebo. It's a little sugar pill that allows patients to believe they're being treated, even when they're not. Among speeders the equivalent is a radar jammer, a device that tricks speeders into believing they're "invisible" to police radar and laser.
Jammers have no benefit in terms of actually jamming radar, but that's not what the promotional materials say. The pamphlet accompanying one device, the Rocky Mountain Radar Phazer II Laser and Radar Jammer, claims it disables X, K, and Ka band radar as well as all laser units, causing police radar and laser guns to remain blank. There's "an FM chirp, a mixer and antenna" that reflect a modified signal to "confuse the computer inside the radar gun," the pamphlet says. It cautions that police radar units might be able to "punch through" this tricky signal within 150 feet and warns motorists to adjust their speeds accordingly.
Most consumers have no way to check the validity of these claims, other than by speeding and risking a ticket. It doesn't work to speed by a roadside sign that feeds back information about vehicle speed because, as the pamphlet for the Phazer II points out, the device won't scramble the roadside signs that "do not have the sampling computer."
"The bottom line is that the so-called jammers don't work," says P. David Fisher, engineering Professor Emeritus at Michigan State University. "Motorists thinking about buying one should consider just putting a block of wood on the dashboard of the vehicle. Doing this instead of buying a device that purports to jam police radar would save a significant amount of money and achieve a virtually identical result. Besides relieving consumers of $150 to $300 for a product that utterly fails to reduce the effectiveness of radar and laser, these devices encourage motorists to speed."
Both Fisher and Institute researchers tested Phazer II, finding no effect on the operation of police equipment to monitor vehicle speeds and identify violators. Installing and operating a Phazer II according to the manufacturer's instructions, researchers drove past police officers expert in operating radar and laser. The researchers made several runs at speeds between 32 and 50 mph, with the Phazer II sometimes turned on and sometimes off. However, police had no indication of whether the device was operating. In each case the officers reported no difficulty measuring the speeds of the vehicles. Nor did they find any reduction in the effective range of their radar/laser units, regardless of whether the Phazer II was on.
Vehicle speeds measured and recorded by the police officers matched the speeds recorded by researchers on the cars' speedometers. The speeds matched for vehicles that were as far away as 300 feet and as close as 150 feet.
Richard Retting, the Institute's senior transportation engineer, points out that "from a safety standpoint, it would be worse if the jammers did work. But just because they aren't effective in shielding speeders doesn't mean there's no safety concern. There is a concern — consumers purchase these devices because they think they can speed and evade detection. Manufacturers encourage this by advertising money back guarantees that promise to pay for fines. So the major concern about the availability of radar jammers is their effect on driving behavior. Obviously these devices encourage speeding."