  A detection system, modeled in a graph, uses "detectors" on a subset of
vertices to uniquely identify an "intruder" at any vertex. We consider two
types of detection systems: open-locating-dominating (OLD) sets and identifying
codes (ICs). An OLD set gives each vertex a unique, non-empty open neighborhood
of detectors, while an IC provides a unique, non-empty closed neighborhood of
detectors. We explore their fault-tolerant variants: redundant OLD (RED:OLD)
sets and redundant ICs (RED:ICs), which ensure that removing/disabling at most
one detector guarantees the properties of OLD sets and ICs, respectively. This
paper focuses on constructing optimal RED:OLD sets and RED:ICs on the infinite
king's grid, and presents the proof for the bounds on their minimum densities;
[3/10, 1/3] for RED:OLD sets and [3/11, 1/3] for RED:ICs.
