Agreed, to disagree.
And though the subject is access to computer contents (instead of a locked safe), I believe the relevance of the DOJ's manual on "Searching and Seizing Computers and Obtaining Electronic Evidence in Criminal Investigations" clearly shows that a computer (or closed and locked safe) in a location subject to a search, would require 'Exigent Circumstances' and a separate warrant.
An excerpt:
"In determining whether exigent circumstances exist, agents should consider: (1) the degree of urgency involved, (2) the amount of time necessary to obtain a warrant, (3) whether the evidence is about to be removed or destroyed, (4) the possibility of danger at the site, (5) information indicating the possessors of the contraband know the police are on their trail, and (6) the ready destructibility of the contraband. See United States v. Reed, 935 F.2d 641, 642 (4th Cir. 1991)."
This report can be found at:
http://www.cybercrime.gov/s&smanual2002.htm#_IC4_
Also, the following regarding a DEA supports the fact that a warrant is required to open a locked safe:
"DEA agents entered Barmes´ home about 6 a.m. Monday. He said that although DEA agents were quiet about what they were looking for, they were adamant about what they wanted him to do. They demanded he open a safe and if he didn´t, "they said they would tear it open," Barmes said.
"They told me that if I didn´t cooperate they would tear up the entire house," he said. "They also said that if they needed to, they would dig up every inch of the 17 acres I have out here. I just gave them the keys to everything so they wouldn´t bust the locks."
Source:
http://www.digitalscale.com/Barmes Article.htm
Finally, it is important to remember that in essence, the Fourth Amendment makes ALL searches and seizures without a warrant presumptively unreasonable and subject to being overcome by certain circumstances. The amendment was created due to concerns that the founding fathers had regarding intrusion into the home: "physical entry of the home is the chief evil against which the wording of the Fourth Amendment is directed". United States v. Watson, 423 U.S. 411 (1976)."
As such, it is best to assume that any warrantless search (as in the case of a locked safe or briefcase) is illegal..... until someone can show that it isn't.
BTW, another good information site can be found at (and NC courts have found that searches of locked briefcases are improper):
http://www.jus.state.nc.us/NCJA/flippo.htm