That's exactly what this does, and it supports multiple levers.
TFS 0.3.6
local levers = {
[5000] = { -- Action ID of lever
area = {from = {x = 100, y = 100, z = 7}, to = {x = 200, y = 200, z = 7}}, -- Area to check for monsters
levelReq = 100, -- Level requirement...