The text below is the counterclaim to the author's thesis statement.
However, when students are aware that lockers are subject to unscheduled searches, they often think of other ways to store their belongings; items are instead concealed in backpacks, pockets, and purses, which are much more accessible to students".
In the text above, the author uses "however" as a bridge to begin his counterclaim and to offer the suggestion that students can hide belongings in other areas besides lockers.