A scope for installing PIR?

["John O" <johno@#no^spam&heathkit.com>]

I need some help from you pros. I'm staring at an assessment question that
says something like this: "when installing a motion sensor in an odd-shaped
room, scope the perimeter and eliminate obstructions."

I'm assuming there is a device that I would look through that gives me some
idea of what the PIR would see. But I can't sniff out anything on the web to
clarify this. I've given this a good try, and far too much time, but I can't
find a link to such a device. Does anyone know where I'd find one?

-John O