A four-in-one safety tool: signal whistle, compass, thermometer and magnifying lens.

Combined tools exist because people carry one thing and leave four at home. This hangs on a pack strap and covers the basics without a pocket full of separate gadgets.

The whistle is the part that matters. Treat the compass as a rough bearing, not a navigation instrument — if you are route-finding, carry a real compass.

Good for a kid's pack, a day hike, or a glovebox.