There seems to be some conflicting advice on the need for tourists to comply with an impending requirement for French drivers to carry breathalyser kits in their vehicles.
Here is a reply to an enquiry seeking clarification from the French Tourist Development Agency.
The word "should" scuppers any idea of a home made solution.
It would seem that the kits are likely to be widely available in garages,supermarkets and motoring outlets in France at about €1. The prices in the UK are pretty high and, it would appear, to be non compliant in the main.
I wonder which breathalyser manufacturer has a relative in the the French legastive?!