A do-it-yourself DUI test?

This post comes from Des Toups at partner site CarInsurance.com.

Starting July 1, you'll have to carry a portable blood-alcohol test kit with you if you want to drive in France. You'll be fined 11 euros -- about $15 -- if you can't produce one when the gendarmes ask.

Who knew such a thing even existed?

Turns out they're about the size of a cigarette, available in the U.S. and much cheaper when purchased in bulk. Expect to pay as much as $7 at a retail counter but as little as $2 when you buy a bunch. We found them at Wal-Mart and suggest you read the instructions before your first drink, just to be safe. (Post continues below.)

The chemically coated crystals inside these single-use devices react to concentrations of alcohol in the user's breath, turning colors above a certain threshold. Most manufacturers sell the devices tuned for "zero tolerance" situations (such as school, they note), 0.05% (the legal blood-alcohol level in France), or 0.08%, the limit in the U.S. (See "Calculate your limit: Avoid a DUI disaster.")

Friends in Europe suggest carrying two: One to use and one to show the police.

Back in the good ol' U.S. of A, while the devices are strictly optional, the $2 gizmo strikes us as cheap insurance if you've had one more than you had planned. They won't tell you anything you didn't already know, but maybe you'll pay attention to the result based on sheer novelty value.

Or you could ignore it and get a fancy, state-mandated electronic model that will ruin your life for the next three years. (See "You can't drive drunk if the car won't start.")

By the way, if your gadget disagrees with a roadside breath test administered by your favorite law enforcement professional, you lose. It won't bail you out of jail, back you up in court or help you dance the SR-22 paperwork shuffle.

More on CarInsurance.com and MSN Money:

• Insuring a salvage-title car: What you need to know
• Does a late payment void my gap insurance?
• Does your car look like you have insurance?
• The most and least expensive cars to insure
• Are stoned drivers safer than drunks?
• Calculator: How much vehicle can you afford?