Only breathalysers marked ‘NF Approved’ are deemed to be legal. There was a shortage, but I am told that they are now readily available at ports of embarkation to France or by mail order from www.alcosense.co.uk/alcosense-singles.html. You need two or three in case you use one. They are cheapest at Carrefour in France, but you have to get to Carrefour first without being nicked for not having one.