The 4th amendment allows for and in certain situations, law enforcement may perform a search when they have a reasonable suspicion of criminal activity (this is documented in the police SM release, even if it falls short of probable cause necessary for an arrest. Under
Terry v. Ohio (1968), law enforcement officers are permitted to conduct a limited warrantless search on a level of suspicion less than probable cause under certain circumstances. In one case, the Supreme Court ruled that when a police officer witnesses "unusual conduct" that leads that officer to reasonably believe "that criminal activity may be afoot". Technically it was witnessed and reported by a witness other than law enforcement, but there is a provisional loophole in the law where the police can conduct a search, including an SD card, in an effort to identify the owner, which could lead to the discovery of criminal activity at which time, law enforcement must stop and obtain a warrant if criminal charges are to be pursued.