Sorry Northerner that was meant to be a "tongue in cheek" comment, didn't mean it as a serious thing, although we were regularly stopped in the 70's and 80's by the French traffic and border police (and the Italians) for minor things that required a small payment to ensure swift onward travel. I don't think that goes on so much now with open borders.
I think seatbelts, air bags, crash helmets (and I remember when none of those were required, well perhaps not crash helmets) are a slightly different thing though. If a system were introduced that stopped you from being able to drive if you had been drinking, and I don't know how that would be policed, then I would perhaps be less cynical about it. However I really don't see how carrying a breath test kit in your car would actually change the habits of those who insist on drinking and driving. After all the law regarding seatbelts requires that you wear the seatbelt not just that one is fitted, similarly with crash helmets. Until this is debated and passed as law, if it ever is, I guess we can only pontificate on what the eventual situation will be.
Whether the French people will be impressed by it also remains to be seen, but I understand that the smoking ban is not adhered to in many rural and out of the way places, very much a shrug your shoulders and carry on as normal attitude which we all love the French for.
Certainly, as I posted earlier, I would not go out and buy a kit until this has become law. For one thing we have no idea what would be required in terms of accuracy.