System Sensor CO-PLATE — retrofit plate that covers the footprint of a previously installed competitive carbon monoxide detector and carries the new CO1224T.It does two jobs at once. System Sensor sizes the plate to hide the outline of the older, bulkier detector coming down, and the plate is also the mounting surface: hold it over the area, use its hook feature to hold the CO1224T on it, then fasten detector and plate together with the hardware supplied in the CO1224T carton, which avoids patching and repainting. CO detector replacement plate to cover the footprint of previously installed competitive detectors Hook feature holds the CO1224T while the assembly is fastened Fixed with the hardware provided with the CO1224T, not with its own fasteners Gamewell-FCI lists the same part for US and Canada, for CO1224T or CO1224A It is an accessory with no sensing element, not a substitute for the detector. System Sensor names the CO1224T as the detector that mounts to it and Gamewell-FCI adds the Canadian CO1224A; the round CO1224TR is not named, so confirm the model before ordering.