A building appliance controller is disclosed that includes a safety feature. In one illustrative embodiment, the building appliance controller may include a controller and a safety element. In some cases, the controller may include a control panel configured to provide an interface, and one or more option cards configured to communicate with the control panel via the interface and to provide additional functionality to the appliance controller. The safety element may include a first relay or other switching element that is configured to selectively pass power to the building appliance. In some illustrative embodiments, when an unsafe operating condition is detected by the control panel and/or the one or more option cards, the control panel and/or the one or more option cards may open the first relay of the safety element to cut off power to the building appliance. In some cases, a safety key may be passed between the control panel and the one or more option cards to help verify the safe operation of the building appliance.