Motorists in France now have to carry breathalyser kits in their vehicles as new laws come into force aimed at reducing drink-drive related deaths.
Drivers and motorcyclists will face on-the-spot fines unless they travel with two single-use devices as part of a government initiative.
The new regulations, which exclude mopeds, will be fully enforced and it is hoped they will save around 500 lives a year.
The rules are aimed at encouraging drivers who suspect they may be over the limit to test themselves with the kits.
Motorists from overseas will have a four-month grace period and anyone failing to produce a breathalyser after November 1 will receive an 11 euro (£8) fine.
French police have warned they will be carrying out random checks on drivers crossing into France via ferries and through the Channel Tunnel to enforce the new laws.
Retailers in the UK have reported a massive rise in breathalyser sales as British drivers travelling across the Channel ensure they do not fall foul of the legislation.
But six out of 10 Britons travelling to France are not aware they have to carry two approved breathalysers at all times, according to a survey by Halfords.
It said it is selling one kit every minute of the day and has rushed extra stock into stores to cope with the unprecedented demand.
Halfords also found one in 10 drivers does not display a GB sticker, risking a 90 euro (£72) fine.
The French drink-driving limit is 50mg of alcohol in 100ml of blood - substantially less than the UK limit of 80mg.
Anyone driving in France must also carry a warning triangle, a florescent safety vest and a fire extinguisher.