The French government has brought in new legislation whereby every vehicle in France must have a breathalyzer onboard, arguably making it much easier for drivers to assess if they've had one too many. This means that millions of drivers in France will have to buy a breathalyzer – together with anyone from outside France wishing to drive in the country. At present, it appears that breathalyzer kits must be NF Approved (the official French ecological certification).
If your kit hasn't been NF Approved, you'll probably face a fine if caught by the Gendarme. However, the likelihood of being checked at all is probably very low, since any inspection requires the police to stop the driver. Checking for broken mirrors or lights, for example, can be done in seconds from outside the vehicle.
There is also the question of when the law will effectively be enforced. While it may become ‘law' by the 1st of July, it has been suggested that enforcement won't commence until November.
At startrescue.co.uk we believe safety is paramount, so if you're heading to France this summer we recommend you do two things: take out short term European cover with us, and purchase an NF Approved breathalyser kit before you go.