[ARCHIVE ANSWER]
If the police have probable cause to search, they will open anything and everything with force, especially safes. In all 50 states, if a cop has probable cause to search an auto, she can search anything and everything whether is locked or unlocked. The rule is when a cop has probable cause (like she smelled weed), then she can search wherever drugs might be located, which is anywhere and everywhere. If the cops have probable cause, they don't need permission to search. In this case, I'm certain the cops had "reasonable suspicion" and asked for permission to search. Reasonable suspicion is less then
probable cause. I made a very good chapter on reasonable suspicion and probable cause in Volume 1: Traffic Stops. Go review it.