A techno-magical device that senses the presence of warp fields at a safe range.
Warp ships, technological interstellar craft, are notoriously difficult to see with normal magical sensors. This would not be an issue except that the interaction of a warp field and a jammer field are mutually fatal. You will never feel it. The chances of a collision are miniscule, but present, and we know about it because it has happened.
Be safe, be covered if you plan to travel anywhere near the Twelve Worlds Empire.
A counterpart device the jammer-finder is made for warp ships.