As of April 1st, 2018, rental properties that have any fuel burning equipment, wood burning fireplace, or an attached garage must have a carbon monoxide detector on every level. Whatever level has a bedroom, that carbon monoxide detector must be in the corridor or hallway outside of the sleeping area. The carbon monoxide detector can be hardwired, plug in, or have a 10-year, sealed lithium battery. 9 volt and AA units will not pass the inspection.