UPDATED 4.59pm Alcohol-activated locks which prevent drink-drivers from starting their car will soon be mandatory for repeat offenders.

LISTEN ABOVE: Dylan Thomsen from AA spoke to Rachel Smalley

Associate Transport Minister Craig Foss confirmed today that anyone convicted of two or more offences within five years will have one of the locks installed in their car.

Those who were caught driving with a reading of more than 3.2 times the legal alcohol limit would also get a sentence which required one of the devices.

At present, sentences which require alcohol interlocks are applied to around 100 recidivist drunk drivers a year.

Now that they are mandatory, they could be applied to between 4000 and 5000 people a year.

The driver will cover the costs of the breathalyser device, which is wired into the vehicle’s ignition. They may get support from a Government subsidy.

Any breath-alcohol reading higher than zero will activate the lock.

AA spokesman Dylan Thomsen said it's about time the policy was introduced.

"Interlocks are the best weapon we have to try and actually stop drunk drivers reoffending. We haven't been using them enough, up until now."

Mr Foss said interlocks had been shown to reduce reoffending rates by around 60 per cent.

"Overseas research and studies have shown that most people that face a sentence like this, do try their best to abide by their sentence and they do start to change their behaviour. That's the real mission here."

He said there will be significant penalties for anyone who tries to abuse the new system - by getting sober people to activate their cars, for example.