Blindsight

Some creatures can discern their surroundings without relying on sight, within a specific radius. This sense is called blindsight. An observer with blindsight can effectively "see" any creature, object, or detail within that radius, regardless of visibility (see Vision and Light) or attempts to hide (see Hide). Blindsight can't discern purely visual phenomena (such as color).

Most forms of blindsight rely on hearing echoes or smelling scents, and are therefore blocked by total cover. Some creatures have a form of blindsight that relies on feeling tremors. Blindsight (tremors) bypasses cover, but it requires the observer and the observed creature, object, or detail to be in contact with the same ground or substance; it therefore can't discern flying, swimming, or incorporeal creatures.