A gate unit includes a gate mount that is adapted to mate with a frame bordering a passageway and formed to include a latch receiver and a gate mounted on the gate mount for pivotable movement about a gate-pivot axis between an opened position opening a walkway passage formed in the gate mount and a closed position closing the walkway passage formed in the gate mount. The gate unit further includes a gate lock configured to lock the gate in the closed position closing the walkway passage formed in the gate mount.