And don’t plead ignorance if you make a mental error. “We’re going to give you the instructions once,” says sheriff’s office Sergeant Darrell Seckendorf, who oversees most Sarasota County sobriety checkpoints. “Then we’re going to demonstrate the test, while saying the instructions again. And then we’re going to ask you if you understand.”

You know you’re really perfectly fine—hardly tipsy, much less drunk. But you wavered and stumbled through both those tests. The officer now believes you to be impaired, and he has other ways to verify that. You’re taken to “the BAT mobile,” the sheriff’s office’s mobile breath alcohol testing van, which is present at every checkpoint in Sarasota. Technically speaking, you can refuse the breathalyzer. But take a look at the clause printed on your Florida driver’s license: “Operation of a motor vehicle implies consent to any sobriety test required by law.” Refuse once and you’ll lose your license for a year—which is actually a civil, not criminal, penalty, because a driver’s license is not considered a basic civil right.

Refuse on two separate occasions, and you’ve committed a first-degree misdemeanor.

A blood alcohol level of .08 or higher is the ball game: You’re legally intoxicated. If your blood alcohol level is lower or you refuse the breathalyzer, the officers must decide then and there if they have enough evidence from their own observations to arrest you.

The traffic unit of the Sarasota County Sheriff’s Office frequently receives statewide recognition for its high number of annual DUI arrests (many officers perform more than 100 arrests per year). In 2006, 1,391 people were arrested in Sarasota for drunken driving. And before you accuse Seckendorf and his crew of having a quota, know this: More than 95 percent of those DUI arrests result in conviction.

But now is not the time to mount a legal defense, says Eger: “If you want to defend yourself, you do it in court, not on the street to law enforcement. If they’re not going to arrest you, they’re not going to arrest you. If they are going to arrest you, nothing good can come of you opening your mouth.”

At 11 p.m., your evening is just getting started. You’re booked on-site and sit in a “jail van” until the checkpoint is closed—usually around 3 a.m. Then you and everyone else who was arrested are taken downtown to the North County jail. You’ll spend a minimum of eight hours in a cell before you’re deemed fit for release.

So what does it take to get to that point of intoxication?

Many variables are involved. Age, weight, sex, drinking habits and the amount of food in your stomach all affect both your blood alcohol level and level of impairment. Drugs—whether prescription or recreational—can interact with alcohol in serious and sometimes unpredictable ways. Warm weather changes your hydration level and enhances alcohol’s effects.

Opportunity factors in, too. “Retirees may have time to sit around and drink all day,” says Dr. Debra Federer, an emergency room physician for Doctors Hospital of Sarasota. “And as you get older, you don’t have the ability to deal with alcohol as well. You start feeling better to the point that you drink more. People really don’t have any idea how much control they’ve lost.”

To explore these variables, we gathered our volunteers—two women, ages 24 and 59, and three men, ages 29, 34 and 51—in our editorial office while Seckendorf and Butler, a breathalyzer expert, set up their equipment. Then we started passing out drinks. Each volunteer had eaten lunch about two hours before, and each drank only one type of alcohol: 1.5 ounces of rum mixed with Coca-Cola, four-ounce glasses of wine or 12-ounce cans of Budweiser. Every half hour, the officers administered field tests and had them blow into a portable breathalyzer. Before the volunteers left with their designated drivers two hours later, we’d all learned quite a bit.

Some people show signs of impairment after just one drink—especially those who rarely drink. Our oldest volunteer (also the lightest in the group, weighing 135 pounds) usually drinks only once or twice a month. After half a glass of wine, she was the first to draw the officers’ attention with increased chatter at an increased volume. She hit .08 after only three glasses of wine. “And keep in mind,” Butler emphasizes, “those were only four ounces each. That’s a lot smaller than a restaurant glass of wine.”