Legislation which makes it illegal to smoke in a car carrying children has come into force in Scotland.
Anyone caught breaking the law by lighting up in a private vehicle with someone under 18 on board now faces an on-the-spot penalty of £100 or a fine of up to £1000 at court.
Smokers' group Forest has branded the regulations "patronising and unnecessary".
But ministers and health campaigners say the move will protect children and take Scotland a step closer towards a target of being tobacco-free within two decades.
Sheila Duffy, chief executive of anti-smoking charity Ash Scotland, said the move sends a clear message that children should grow up in a smoke-free environment.
She said: "The most recent data shows that about one in six 15-year-olds are sometimes or often exposed to second-hand smoke in the car.
"When we know that just one cigarette can quickly lead to harmful levels of smoke, we have to take action. This is about protecting children's health.
"Similar laws are fast becoming the norm around the world, from Australia and Canada to the United States, France and Ireland. Scotland's children deserve the same protection."
The Smoking Prohibition (Children in Motor Vehicles) (Scotland) Bill was passed unanimously by MSPs almost a year ago.
It was introduced to the Scottish Parliament by Liberal Democrat MSP Jim Hume.
He said: "It fills me with great pride that through hard work and cross party consensus we are now seeing the introduction of a law which can potentially save 60,000 children a year from the hazards of second-hand smoke."
Paying tribute to his own mother Joyce, a non-smoker who died from lung cancer five years ago, he added: "Thanks to all those in support of this measure, we have taken a huge step in the right direction to having a healthier Scotland for all."
Second-hand smoke can cause conditions like bronchitis, pneumonia and asthma and research shows the toxic particles contained in the smoke can reach harmful concentrations within a minute of lighting a cigarette in a car.
The Scottish Government said the measure is part of its plans to create a "tobacco-free generation" by 2034, defined as a smoking rate of less than 5%.
Public Health Minister Aileen Campbell said: "Our target to reduce the proportion of children exposed in the home from 12% to 6% by 2020 has been met five years early.
"The ban on smoking in cars will help to build on that success by reinforcing the message that the toxic fumes from cigarette smoke are harmful - particularly to children."
But Simon Clark, director of smokers' group Forest, said: "The regulations are patronising and unnecessary. Very few adults smoke in cars with children. Smokers know it's inconsiderate and the overwhelming majority don't do it.
"So few people smoke when there's a child in the car it will be like looking for a needle in a haystack."
He added: "The law is a classic example of virtue signalling. It's utterly pointless and a complete waste of time and resources that could be better spent elsewhere."
A law banning smoking in vehicles carrying children came into force in England and Wales in October last year.