There is already a fair amount of confusion over what is required; hopefully the following FAQ will help:
Q. What do i need to carry?
A. You need to carry a French NF-Approved Digital Breathalyser or Breathalyser Kit. A disposable Breathalyser Kit is the cheapest solution at £3.00 Inc VAT. The French Police are suggesting vehicles carry at least two, so that if one is used by the driver, a second remains for inspection but the law requires either an NF Approved digital breathalyser or one unused breathalyser kit.
Q. If the Police think think I've been drinking, will I have to use my kit or will the police use their own breathalyser to test me?
A. No. The Gendarme will NOT ask you to use your own kit - you simply have to carry a kit in the vehicle, the same as you need to carry a Hi Vis Jacket & Warning Triangle. Digital (i.e. reusable) breathalysers: At present there are very few low-cost NF Digital Breathalysers as a majority that have approvals are full Police-Spec devices.
Q. What is "NF Approval"?
A. It's an approval process run by the French Government and results in the Breathalyser being given a certificate.
Q. What if my Breathalyser isn't NF Approved?
A. Then unless you're really lucky and come across a very friendly Gendame, you will could be fined. To be approved it MUST have a bag to blow into and it must have the NF logo on the packaging like this: