Most people instinctively understand the concept of privacy.
It's the freedom to decide which details of your life are public and which are not. At the same time, most of us acknowledge that society is served when the police, in appropriate circumstances, are allowed to look for and seize contraband, stolen goods and evidence of a crime. A police investigation is not a search unless it intrudes on a person's privacy. Therefore, if the police install a hidden video camera in a public restroom, the action is considered a search and must meet the Fourth Amendment's requirement of reasonableness. On the other hand, if the police glance into a car and see a weapon on the front seat, it is not a search because it is unlikely that a person would think that the front seat of a car is a private place.