So, it's often been said that stealth in space is impossible because

A) Thrusting would give you away from across the solar system
B) Crew need to live at a comfortable temperature and the heat radiation would give you away. If you had an active generator that would DEFINITELY give you away.
C) Ships are big and can be spotted by Radar and star occlusion even if you somehow mask their heat signature

But what about a small spy drone fired from a coilgun, something operating just above the ambient temperature of the universe? Maybe something as big as the size of a pea. How would this be even remotely detectable?