Function sensor 

pub fn sensor<'a, Message, Theme, Renderer>(
    content: impl Into<Element<'a, Message, Theme, Renderer>>,
) -> Sensor<'a, (), Message, Theme, Renderer>
where
    Renderer: Renderer,

Creates a new Sensor widget.

A Sensor widget can generate messages when its contents are shown, hidden, or resized.

It can even notify you with anticipation at a given distance!