Does an officer have to have a warrant for every locked door in home?

No. The warrant will spell out the area of the search (a home, a car, a separate garage, any sheds or outbuildings). A search warrant will allow a search in any area where the contraband may reasonably be concealed. Example: An AK-47 is sought. The officers may not look inside a 5" x7" jewelry box. However, any spaces large enough to hold or conceal such a weapon may be searched (e.g.: closets - large bureau drawers - under the bed - between the mattresses - etc)