It's certain magical things that are active on both astral and physical plane. Astrally perceiving mages or adepts, active foci or spells, certain critters (like those bargests we met in the mountains), materializing spirits and things like that.
So as mage or adept if you remove all your foci (and we don't have any) and don't have active spells on you (which we haven't), you should be fine as long as you stay on the physical plane.
Wards of course also stop fully astral movement, so we can't sneak in that way.