The courts will look to the facts to determine if the search was legal. While the police may generally only search pursuant to, and within the authority conferred by, a warrant, the courts will not throw out evidence which the police found in good faith, reasonable reliance on the warrant and its power,  even if it turns out they exceeded or went beyond the warrant--the key is, the police *must* have acted reasonable and logically and in good faithSo, say that someone was home at the time and informed the police that the lockbox belonged to somone else (e.g. a guest), or the lockbox had another person's name, etc. on it: in those cases, since the police were given information that the box did not belong to the person whose home they were searching, they should not have opened it. Possibly, they could have temporily impounded it or had an officer secure it while seeking a new or amended warrant to allow it to be searched (i.e. they could have made sure that it or its contents was not removed while seeking a warrant for it), but still, if there was credible evidence that the lock box was not covered by the warrant (as not being a part of the home and not belonging to the homeowner), it should not have been searched.On the other hand, if there was no reason for the police to at the time know that the lock box belonged to a guest, they could have searched it, as being part of the home. Since they acted in a reasonable, good faith manner, it is very unlikely that a court would later throw out the results of that search.