Could this style of compass in the link be used to detect ghosts ?
http://www.overstock.com/Sports-Toys/BTOutdoor-Military-Engineer-Style-Lensatic-Compass/2176660/product.html?
A liquid filled compass will work, but it’s not your best bet. It causes too much resistance due to the friction of the liquid. A dry compass will give you much better results!
Land Navigation – Lensatic Compass and Map Use