Collision without actual physical collision?

Ok, so I have an object in blender set to invisible, and I have it so if any other objects touch it, they float up. But I want the objects to be able to go through the invisible object, as if it were a ghost, yet still trigger the collision action. Thanks in advance :o

I think the object type must be sensor. I’m not sure.

Ok I have just about given up with this, I changed it to sensor which seems to be what I want, but it still doesn’t work. :confused: Heres the blend if anyone can help (yes that is the bathroom scene, its just a test I’m not actually using it in anything.)