No, law enforcement does not always need a warrant to seize property. A police officer can seize property if he or she is in the process of arresting a person or conducting a lawful search, or if the officer conducts a search with your permission.
However, if property is seized without a warrant, the officer must have “probable cause” to make the search that leads to the seizure. This means that before being searched by an officer, there must be facts that would lead a reasonable person to think that a crime had been or was about to be committed.