As from 1st January 2016 (not March 8th 2015), all properties in France must have a smoke detector installed. If you are a landlord, you have to install a smoke detector in each flat / house you own. If you are the tenant, you are responsible for the maintenance of it (ie you must replace the batteries when need be).
Smoke detectors don't have to be wired in, they can just be batterie ones.
This applies also for furnished and unfurnished properties in France.
Make sure you buy a smoke detector which has the NF sign on. You will easily find some in DIY shops in France.
Our fire alarms were fitted the day we bought our French house 12 years ago, so I won't be rushing to the DIY shop! We are already complying to the French regulations.