If some UAP are nonhuman technology, they might belong to an autonomous system stationed near Earth long ago. It would need no repeated interstellar trips; its creators could be distant, absent, or extinct. SETI research offers precedents, but an observer would not by itself prove an ancient factory, a protective mission, or an ability to influence consciousness. 1. A presence that outlives its creators The Sentinel Probe Hypothesis proposes that a nonhuman system reached our solar system and...