Ok, i dont know if this is because of the new update or what.

 

I use the device, it tells me to go all over varrock castle, then i end up having it point to a wall, or a bed, or a crate #-o . I do not understand how to use this thing. If someone could please help me, i really need it...

Carefully utlise your minimap to look out for yellow dots that are not supposed to be there. Like in the altar room inside the castle where there usually isn't anyone inside and you spot a yellow dot there from minimap, that dot may be bob.