A high-pitched shriek comes through the speed radar, red lights blink and bounce on the screen, and motorists press their brakes in the hope of avoiding detection.
But it is too late. They have been caught.
The speeds differ - 108kmh, 110, 116 - but the reasoning is always the same: "I didn't realise I was speeding''. Or words to that effect.
It was a familiar theme over the five hours I spent with Sergeant Graeme Evans, of Otago coastal's road policing group, yesterday.
Despite those ticketed being well-spoken, in safe and roadworthy cars and licensed to drive, they were still willing to risk their lives - and the lives of others - to shave a few minutes off their journey.
Research shows increased speed is directly linked to fatalities in crashes. A driver involved in a crash with an impact speed of 80kmh is twice as likely to die as one in a crash with an impact speed of 64kmh.
"This is one of the most dangerous things we do as a society," Sgt Evans says.
"We are doing nothing more than sitting in metal coffins.''
It is a sombre thought but this is a man who has seen the reality of car crashes - the sight of twisted metal, the sound of pain, the potential cut short and the families forever broken.
The extra kilometres of speed are not just figures on a graph, but a tangible difference in cause and effect.
"It's funny the things that stick with you,'' Sgt Evans says.
"Like the smells. It might be brake fluid and you go to get your car serviced at the garage and you smell it and something might come back.
"I don't wake up in nightmares or anything, but, I suppose, it does get in.''
Worse still was relaying the news to loved ones.
"It's pretty commonly accepted across my colleagues ... It's the absolute pits when you get the job to go and tell the relatives,'' he says.
"You'll rehearse it all you can.
"You will prepare it all in your head, but it all goes out the window once you knock on the door.''
The motorists pulled over for speeding during my time with Sgt Evans - six in five hours - are all wilfully ignorant of the danger they have created for themselves and, in many cases, their loved ones in the back seat.
Saul Uren, of Nelson, is caught travelling 108kmh coming uphill between Waikouaiti and Waitati.
He admits there's "no reason at all'' why he is speeding and is aware a reduced tolerance is in place for the Easter weekend.
As soon as the lights appeared in his rear-view mirror, he knew he had been caught after "creeping over'' the speed limit.
"I know it's strange to say I'm a responsible person when I have just done something irresponsible, but generally I'm a responsible person,'' he says.
"I'm not justifying speed, but I'm not a reckless person.
"It's not nice [being pulled over] and of course it's not nice if something happens while you're speeding.''
He is sent on his way with a ticket for $30, a greater appreciation for his speedometer, and a greater awareness of the many other officers policing the roads between Dunedin and his final destination, Nelson.
He is not alone in being unaware of his speed; it is the same reason used by the other motorists pulled over.
It is why Sgt Evans tries to take an educational approach to law enforcement. He does not hide around corners or in the shadows and he is not waiting to pounce on motorists coming downhill in passing lanes.
"I don't just pick you out of thin air because I have got nothing to do and I'm bored, and I don't have a quota,'' he says.
"We can't prevent every crash but being as vigilant with speed as we can, then at least if there is a crash the harm is reduced.''
He believes a change in mindset is needed among New Zealanders.
"We need to think about the speed limit as a limit rather than a target.''
"Pull your speed back and the less harm there's going to be.''