DB
...... but you can only use that alerting system overwater - right! To attempt to use it over land would be to compromise your attention on the REAL reference for DA - the BARALT.
As Crab said earlier, the Radalt can only give you info about the terrain directly beneath the aircraft. At 200 feet on an ILS to an (overland) airport your are roughly 0.65 nm from the touch down point. Unless I am very much mistaken That would put many DA's outside the airport boundary where terrain could be a valley or contain buildings.
G.