"The home is inviolable.-- Searches may be authorized only by a judge or, when time is of the essence, by other authorities designated by the laws, and may be carried out only in the manner therein prescribed."
According to this article, homes (private spaces) are protected-- nobody is allowed to enter an apartment without permission or eavesdrop on the residents or put them under surveillance. Same applies to all private spaces, whether it is an apartment, a house, a tent, a room in a shared accommodation facility, etc.
But there is one exception: In an emergency, the Fire Department or emergency doctors can come into the apartment even against the residents' preference. Furthermore, if a person commits a crime at home (or plans to do so), the police can enter the place. In principle, however, police need court permission to do so. The police may only enter the apartment without a court permit if it is entirely unavoidable. For instance, if someone calls the police to inform them that they have heard loud cries for help from the neighbouring apartment. In cases like this, even if the people in the apartment next door do not open, the police can and will enter the apartment.