In United States v. Carriger, 541 F.2d 545 (6th Cir. 1976), the court held that a tenant in a multi-unit apartment building had a legitimate expectation of privacy in the stairway of the building.
The building in question was locked and only could be accessed by a key or if the entrant was buzzed in by a tenant.
The police managed to gain entry through the open door after several workmen exited the building.
Once inside, they observed a suspected drug transaction that formed the basis of probable cause for their entry into an apartment in the building.
The court held that, "when, as here, an officer enters a locked building, without authority or invitation, the evidence gained as a result of his presence in the common areas of the building must be suppressed." Id. at 552.