Should or should not put mezuza in elevator lobby on your floor (considering that has 4 x 4 amot and is Jewish only)?
According to many authorities there is no obligation to place a mezuzah on an elevator door. However, some dispute this, and doing so is therefore worthy practice.
Rav Shlomo Zalman Auerbach writes (Minchas Shlomo 2:100:5) that there is no obligation of placing a mezuzah on the entrance to an elevator, because it moves from place to place and is therefore a “ladder” and not a “room.” He also discusses a stairwell, and concludes that it is worthy to place a mezuzah at the entrance to a stairwell – but does not say this about an elevator.
On the other hand, we find in the Minchas Yitzchak (4:93) that the obligation of mezuzah applies even to an elevator.
Orchos Rabbeinu (3:additions to p. 172) cites that the Steipler maintained that the elevator is exempt from a mezuzah, and also cites from Rav Moshe Feinstein that he was not careful to place a mezuzah on an elevator door, as cited also in Ohalei Yeshurun (2:note 66; see also Betzeil HaChochman 3:80 who writes that there is no obligation, and see Lehoros Noson 3:72-3).
Chovas Hadar (5:11) writes at length on the subject, and writes that one should put up a mezuzah on the right of the entrance to the elevator on the first floor, and on the left on all other floors. He even writes that where the elevator lobby has 4 by 4 amos, a berachah can be made.
However, due to the opinions noted above, one should not recite a berachah in this case.