Decoy can not be sent to an unexplored hex.
4.2 Movement restrictions wrote:
Units without an Attack Strength (such as Colony Ships, Decoys
and Miners) may not enter a hex with a face-down (unexplored)
System marker, enemy unit, or enemy colony unless a combat
capable ship also enters that hex (it need not have started in the
When you use the Exploration tech you can remove the Danger! marker or leave it face down.
9.8 Exp loration Technology wrote:
The player has the choice of returning the marker face down
or revealing the marker. If the marker is revealed and it is a marker
with a one time effect (Danger!, etc.), it is removed.