I have an MS10? x10 motion detector in the stairwell on the way down to the basement. It is to turn on the light at the bottom of the stairs when it sees one of us. When it's good it's very good. But the x10 wall switch has always been the first to go when there are too many switching supplies in play in our home.
Crazy thing is though, is that I know when it's not going to work because the motion detector won't blink n' flash.
If I unplug the offending noise makers so that the wall switch will work, then the motion detector will do it's blinky blinky and the light comes on.
As far as I know the motion detector being battery operated is completely stand alone and only an output device. But darned if when the wall switch is not going to work, the motion detector seems complicit and will not see you. I know it's not batteries as I'll see this action change over the coarse of a week without any change other than laptop chargers and humidifiers being unplugged.
Boo-boo buddies.