A wall switch lockout device for selectively limiting access to a wall switch relative to which the wall switch lockout device is mounted, the wall switch lockout device comprising: a mountable base having a front face and a rear face, the mountable base having a switch opening extending therethrough from the front face to the rear face for receiving the wall switch therethrough; wherein the mountable base includes a base rail (42a, 42b) and a base guide (44a, 44b); a cover positionable and securable over the front face of the mountable base for selectively covering and limiting access to the switch opening; a pair of mounting openings (26a, 26b) for mounting the mountable base; and a pair of inserts (14a, 14b) received in the mountable base and slidable relative thereto; wherein the pair of inserts (14a, 14b) includes an insert rail (48a, 48b) and an insert guide (50a, 50b); wherein the insert guide (50a, 50b) of the pair of inserts (14a, 14b) is attachable to the base rail (42a, 42b) of the mountable base and the insert rail (48a, 48b) is attachable to the insert guide (50a, 50b) such that the insert is slidable relative to the mountable base along attachments between the insert guide (50a, 50b) and the base rail (42a, 42b) and between the base guide (44a, 44b) and the insert rail (48a, 48b), wherein both of the insert guide (50a, 50b) and the base guide (44a, 44b) include retaining projections (46a, 46b, 52a, 52b) such that the insert guide (50a, 50b) and the base guide (44a, 44b) is snappable onto the respective base rail (42a, 42b) or insert rail (48a, 48b); and wherein at least one of the pair of mounting openings (26a, 26b) is on the at least one insert such that, when the at least one insert (14a, 14b) is slid relative to the mountable base, a hole-to-hole distance between the pair of mounting openings (26a, 26b) is variably adjusted. a mountable base having a front face and a rear face, the mountable base having a switch opening extending therethrough from the front face to the rear face for receiving the wall switch therethrough; wherein the mountable base includes a base rail (42a, 42b) and a base guide (44a, 44b); a cover positionable and securable over the front face of the mountable base for selectively covering and limiting access to the switch opening; a pair of mounting openings (26a, 26b) for mounting the mountable base; and a pair of inserts (14a, 14b) received in the mountable base and slidable relative thereto; wherein the pair of inserts (14a, 14b) includes an insert rail (48a, 48b) and an insert guide (50a, 50b); wherein the insert guide (50a, 50b) of the pair of inserts (14a, 14b) is attachable to the base rail (42a, 42b) of the mountable base and the insert rail (48a, 48b) is attachable to the insert guide (50a, 50b) such that the insert is slidable relative to the mountable base along attachments between the insert guide (50a, 50b) and the base rail (42a, 42b) and between the base guide (44a, 44b) and the insert rail (48a, 48b), wherein both of the insert guide (50a, 50b) and the base guide (44a, 44b) include retaining projections (46a, 46b, 52a, 52b) such that the insert guide (50a, 50b) and the base guide (44a, 44b) is snappable onto the respective base rail (42a, 42b) or insert rail (48a, 48b); and wherein at least one of the pair of mounting openings (26a, 26b) is on the at least one insert such that, when the at least one insert (14a, 14b) is slid relative to the mountable base, a hole-to-hole distance between the pair of mounting openings (26a, 26b) is variably adjusted.