While it is law from today it appears that there will be a period of grace up to November the 1st until it will be enforced.
I cannot believe that these kits that only cost 2 or 3 euros can give an accurate reading and personally I think it could result in some people relying on them when in fact they shouldn't be driving.
I may be cynical but it appears that Mr. Daniel Orgeval, the president of the road safety lobby group that was responsible for persuading persuaded the previous government to adopt the law is also a senior director of one of the only two companies licensed to produce the kits!