There is an obj_sensor in the sim file of the stock land units.
I assume it's a Visual sensor as I've not really checked the ID's
The Land units use AICostalDefense. Note the spelling.
I'm wondering about a strange thing in the GR2 files on them though.
GrannyViewer lists 3 Bones but only 2 appear and there seems to be no connection to the missing Base Bone?