At the Place d'Armes, next to the Rampe de la Major is a beautiful one-storey building hosting a department of the local police. We saw several police officers entering and leaving the building, so it's definitely an active police station. A sign on the long side of the building says "Commissariat de la Condamine, Police, Principauté de Monaco".
According to some online ressources the police station was renovated in 1956 (the Then photo) on the occasion of the marriage of Grace Kelly and Prince Rainier of Monaco and once again in 2015.