Sennett Devermont styles himself the drinking crowd's Batman, working to keep Los Angeles drivers out of trouble if they're thinking of drinking and then weaving their way home. Mothers Against Drunk Driving contends that Devermont is more like the Joker.

He's in their sights because he has nearly 42,000 Twitter followers and more than 20,000 text subscribers. Many thousands have downloaded his free app, MrCheckpoint, which provides frequent daily updates on the locations of police DUI checkpoints scheduled throughout Southern California.

Devermont, 25, who lives in Santa Monica and works out of various L.A. coffee shops, already has a huge fan base to whom he has sent 1 million text messages since last summer. But the app he created in 2012, at MrCheckpoint.com, might go truly stratospheric now that Deborah Hersman, chairwoman of the National Transportation Safety Board, has called on states to dramatically slash the legal limit for drivers' blood alcohol content from .08 percent to .05 percent.

Devermont argues that text messages sent by his app and tweets from @MrCheckpoint are not intended to help revelers steer around the law. Instead, he sees MrCheckpoint as an efficient preventive tool that stops impaired drivers before they get behind a wheel.

The courts have ruled that, as a matter of drivers' constitutional rights, police must publicize the inspection locations beforehand. By warning drivers in Los Angeles, San Diego, Riverside, San Bernardino and other cities where and when DUI checkpoints are expected, Devermont gets many drivers to think about either staying home to party, finding a designated driver or calling a cab.

MrCheckpoint got started with tweets to friends, “and it has grown organically,” he says. “I have spent no money on advertising.” People learn about it through Twitter, as well as Facebook and other social media.

He sends out alerts nightly beginning at 7 p.m., using information supplied by Los Angeles Police Department, L.A. County Sheriff's Department, San Diego Police Department and other police agencies.

Fans can access MrCheckpoint by texting NODUI to the number 51515. A greeting pops up that, before displaying the DUI checkpoints in your area, requires you to check a box agreeing not to drink and drive. “It's on the honor system,” Devermont says.

The seeds of his innovative idea were planted during his first year at San Diego State University, when police singled out Devermont, then 18, for underage drinking at a party. He was told he'd failed a field sobriety test, yet he hadn't had a single drink. When police insisted he take a Breathalyzer test, the machine registered zero.

“It was humiliating and intimidating. I felt violated,” Devermont recalls. “After that, I looked up my rights.”

He learned that police cannot require a field sobriety test, that refusing the test is not an admission of guilt and that, at a checkpoint, you're not obligated to answer any questions put to you by police.

Then, in July 2011, Devermont was ordered out of his car at a San Diego Police Department checkpoint. He videotaped the entire episode and says he caught San Diego police blatantly violating the law.

After Devermont initially refused to get out of his car, he recalls, the officer “told me to get out, and I did, and he took me aside while another cop entered my car — and went through my wallet. I have that on film. That was after I had already given them my driver's license. I blew a zero and they let me go. Again, it was humiliating. He had me in handcuffs and the other officers were treating me like a criminal.”

Devermont's attorney, Mary Prevost, says, “We're throwing the kitchen sink at them for violating his civil rights. … We're suing for false arrest, emotional distress, battery [tight handcuffs], searching his personal belongings. The city is treating him like: 'Why didn't you just waive your constitutional right not to answer questions from the cops?' The cops were saying that Sennett was being a shitty citizen for not waiving his rights.”

Prevost predicts that the San Diego city attorney will “spend $50,000 to defend their cop instead of giving my client $5,000.”

Five months later, following a dinner in Santa Monica with his parents, Devermont made an illegal right turn on red onto Santa Monica Boulevard. He was pulled over by Santa Monica police officer Kobe Arnold and refused to perform a field sobriety test. He was arrested.

Again, troubling things began to happen. His car was impounded — and his dogs, in the backseat, were sent to the pound. At a Santa Monica hospital, his blood was drawn. Then he was hauled to lockup and spent a night in jail. The next day, Devermont says, he had to pay $1,000 to get his car and dogs back.

Two months later, his blood test proved negative, and prosecutors declined to file charges.

MADD has little good to say about Devermont. “We don't want apps out there that allow people to evade checkpoints,” Anna Duerr, MADD's director of communications, says. The organization's executive director in Los Angeles and Ventura counties, Pat Rillera, explains, “While we support the publication of checkpoints as a deterrent to drunk driving, sites like MrCheckpoint alert drunk drivers so they can evade arrest. It's not meant as a positive.”

Devermont says they just doesn't get it. “I want to make MrCheckpoint the next-generation MADD. Since August of last year, we have sent out more than 1 million text messages helping identify these checkpoints. … Here's one of the things I tweet all the time: 'If you can't afford a $40 cab ride, you can't afford a $10,000 DUI.' ”

Devermont's Twitter and Facebook accounts are flooded with thanks from people who decided to stay home or handed their keys to a sober friend. They send photos showing themselves enjoying an evening on the couch or being driven around.

Lt. Shan Davis, Beverly Hills Traffic Bureau commander, once met Devermont — at a DUI checkpoint. He thinks what Devermont is doing “is a great thing. … If we can get people thinking about these checkpoints so they're not driving drunk, then it's good. Take a cab, or give your keys to a friend.”

Or put out the bat signal. One of MrCheckpoint's online advertisers is peer-to-peer rideshare company SideCar, whose app matches people needing rides with those willing to give them. Sidecar's Los Angeles manager, Drew Crofton, says, “We're … 20 to 30 percent less than a regular taxi. The app is free, and you pay the suggested donation.”

While MADD is critical of Mr. Checkpoint, its attitude is not universal. Allen Porter of drinkinganddriving.org, which advocates sober driving, is a big fan. He says MrCheckpoint “gets young people talking about not just the checkpoints but the dangers of drunk driving.”

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