A fastener for communication lines includes a flat metallic body having an opening for a metallic mounting screw. A distal end of the body is configured to capture a line previously installed along a building surface via an adhesive or other non-metallic fastener. A cover has an open top, and a bottom wall having an opening that aligns with the opening in the fastener body when the cover is disposed over the body. The screw is inserted through the top of the cover, and the openings in the bottom wall and the fastener body, to mount the fastener body together with the cover at a position on the building surface where the fastener captures the line securely. The line is thus prevented from collapsing and interfering with responders if the adhesive fails during a building fire. The fastener is concealed by closing the cover top with an associated cap.