  Foucaud, Krishna and Lekshmi recently introduced the concept of monitoring
edge-geodetic sets in graphs, and a related graph invariant. These are sets of
vertices such that the removal of any edge changes the distance between some
pair of vertices in the set. They studied the minimum possible size of such a
set in a given graph, which we call the monitoring edge-geodetic number.
  We show that the decision problem for the monitoring edge-geodetic number is
NP-complete. We also give best-possible upper and lower bounds for the
Cartesian and strong products of two graphs. These bounds establish the exact
value in many cases, including many new examples of graphs whose only
monitoring edge-geodetic set is the whole vertex set.
