I'm pretty sure some early versions of Ritter's PSK were packed with the compass next to some metal, so that it didn't work while in the pack. At the time it was said that not only would it start working as soon as you took it out of the pack, but that no long term damage would come from it being stored so close to metal. (They changed the packing anyway.)

There was a thread here, but I got nowhere searching for it.