DUI checkpoints are illegal in the sense that they are clearly violative of the 4th Amendment's prohibition against illegal search and seizure. The U.S. Supreme court conceded that they are violative of the 4th, but authoriezed them nonetheless as an exception justified by public safety. The "minor intrusion" on the traveler's journey along a public highway is outweighed by the benefit to society as a whole in curtailing drunk drivers.
I disagree with the U.S. Supremes.
I particularly liked one statement uttered several times by this driver: "Am I free to go or am I being detained?" Whenever a police officer confronts someone, whether it is at a DUI checkpoint, on the street or wherever, the officer will refer to it as a "consensual encounter," engage the person in general conversation and then ask more direct questions "do you have anything illegal on you?," etc.
As soon as the cop says, "Hi, how ya doin'?", you should say, "Pretty good, officer. Am I being detained here, or am I free to go on my way?" If he says you are being detained, you are then entitled to a Miranda warning and are not obligated to answer any questions. (You're not obligated to answer any questions anyway, assuming there was no probable cause for the encounter.) If he says you are free to go - go.
What's really quite amazing is the response of some who don't care that checkpoints of any kind within the interior boundaries of the United States are in fact, as acknowledge by the Court, per se violations of the Fourth. Worse, is their attitude toward those who will not tolerate being harassed by questions.
BTW, that's my standard answer.
I've only been through one DUI checkpoint. The officer knew the law and responded professionally when I told him that I don't answer questions put to me by police officers.
"Why not?"
"Like I said, officer, I don't answer questions."
"I'm just trying to ensure your safety and that of the public." [I must say, that was a very smooth comeback.]
"I'm just wondering if I'm being detained or if I'm free to go."
To which he smiled and said, "You're free to go."
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Now, in San Diego, I ran into a real arrogant cop, young and arrogant, bad combination.
I was walking my dog in Balboa Park outside the designated area. I didn't know that at the time being an out-of-towner unfamiliar with local ordinances. Where I live there's no such thing as designated areas to walk one's dog, though there are enclosed designated areas to let one's dog off the leash in parks.
Anyway, dude's really aggressive about it. "Hey, dumbass, what do you think you're doing?"
I turn around. A badge is walking toward me. I look at the leash, my dog and back at him.
"Get your dog out of here now."
I start to walk away toward my car. I surmise what the problem must be. Why talk about it? He told me to leave. What do I care? The dog already peed.
"Where the hell you going?"
I point at my car, the only one around at that end of the lot.
He's walking toward me again. I can tell he's pissed because I won't speak.
"What's your name?"
"Am I being detained or Am I free to go?"
Now he's really pissed.
"Give me your ID."
"Why?"
[My wife has the camera out now and is filming from behind the windshield. He doesn't see that. Never go anywhere without it!]
"Okay, smartass, I was going to let you go, now I'm going to cite you."
"Your name and badge number will be on the citation?" [I'm audio recording on my phone, by the way, a handy little feature.]
Don't recall what he said to that, but it wasn't nice. More verbal abuse.
"You're out of state? This is your real name and current address?"
"That's right."
[Now he notices my wife and the camera.]
"Tell her to turn that off."
"Not a chance in hell, and I'm audio recording. There's no wiretap law in California prohibiting it. You have no more expectation of privacy in public than I do."
That's when his tone changes. No citation after all. I wouldn't have paid it anyway, just sent a copy of the recordings to the respective courthouse . . . from another state.
True story.
I imagine this clown has gotten a lot of complaints, and that's the main reason he backed off.