The seeker was a reconnaissance device developed by the Xindi-Reptilians originally for use in the Xindi Civil War. It incorporated anti-gravity technology to fly and seek out enemies and then report back to its operator. It, like much other Xindi technology, incorporated biological components – so much so that a Starfleet scanner could actually mistake it for a Xindi bio-sign.
The Reptilians attempted to use a pair of seekers to locate Gralik Durr on the Xindi-Arboreal colony, but one was destroyed by Enterprise personnel. The other escaped to report in, but its scans were not definitive enough for its masters to reach any conclusions. Gralik claimed that he had destroyed the first seeker because it was frightening the tree scarabs he was hunting. (ENT: "The Shipment")