What would deter you from speeding? How about a loud, jarring, and utterly annoying noise emanating somewhere from outside your vehicle?


The LRAD sound cannon, a "directed-sound communication device" that can blast sound waves over long distances, has been used everywhere from the war in Afghanistan to Occupy Wall Street. Now it's being deployed by the Missouri Department of Transportation to slow down speeders.

Think of it as an audible version of those digital signs that display the speed limit followed by "YOUR SPEED." But, instead of a flashing number, you hear the sound of a ray gun. Or maybe even someone's authoritative voice warning you about "slow vehicles ahead."

According to MoDOT, the first transportation department to use LRAD like this, the systems will be set up around highway construction sites, either placed along the roadside or on the back of construction vehicles. Using radar, the sound cannon is only triggered by speeding vehicles and can emit up to 153 decibels of noise directly at the moving target, according to MoDOT employee Michele Compton. "The sound easily penetrates the windshield and well-insulated cab of a car, even overriding the vehicle's engine sounds and a radio turned up loud enough to jam to tunes at highway speeds."


As I mentioned before, the LRAD is no stranger to law enforcement, who use the cannons to placate unruly crowds or make emergency announcements. But LRADs are known as "acoustical weapons," designed to disturb and disorient people—not exactly the kind of thing you want to do to someone operating a vehicle. I think I'd be pretty terrified if I heard a noise like this while cruising down Interstate 70.

Plus, there has been evidence that sound cannons can cause permanent hearing damage at rates over 130 decibels. I would guess that DOT workers would already be using ear protection, but you've gotta wonder about the dude in the Miata convertible who's unprepared for that LRAD hidden up ahead. [Jalopnik, Storyleak via Alex Goldmark]