Hello, I have my ring outdoor camera looking over over the lawn. I also have a robot mower machine. I set the motion settings at 1 and activated the person recognition option. I keep getting alerts all night when the mower passes in front of the camera.
Hi @Agis07. Depending on the size of the mower, it may trigger a motion event regardless of if you have People Only Mode on. People Only Mode can help you refine your motion alerts, but it will still register motion from movement in your Camera’s view such as in the case of a mower moving in front of the Camera every night. You can read more about motion detection in Ring devices and how it works in our Help Center Article here. You may want to consider repositioning your Camera to get less of your lawn in view to cut down on alerts from the mower. 
I have this issue too and I think I have an idea that could work.
Maybe some kind of decal with a pattern or maybe an IR reflector that could be affixed to the mower could be designed and then the camera can be re-programmed to ignore that “image” when it’s in the field of view.