If you do use the M-Button, there are specific conditions to require it to function properly. Like, installed within
steel bars to isolate any signal interference. I personally do NOT use it, as I have found it to be prone to issues and the convenience is outweighed by a much more simple directly wired scheme.
As a matter of fact, if you have not bought it yet, and want one, PM and address. I have several on the shelf I'll happily send along as a gift. No returns, no complaints, no finger-pointing later