DO NOT leave your car parked on the street with any valuables (even if they are not visible). After a recent theft & discussions with police & locals (we live in France), we discovered that petty theft & burglary, including in hotels, is on a massive increase in Nice. At the police station where we filed our complaint there were persons who were robbed on the train, in the street, & in their hotel room (not hotel staff, but persons breaking into the room).
Our car has an alarm & we stopped just for lunch, next to a major hotel on the Promenade des Anglais (a busy area). It was a spur of the moment decision on our return after a few days holiday in the south, & we foolishly forgot our own rule: ALWAYS park in a parking facility with video surveillance if there are valuables in the car. Even then its not a guarantee of protection, but it increases it. Our car has been burgled 4 times in the past 12 years, and never in a parking lot.
So, be attentive!