The alarm clock. The personal computer. The smartphone. The radio. You know the greatest gadgets of all time (and you’ve probably owned most of them), but which has changed the world more than any other? To make the latest issue of Popular Mechanic magazine’s list of 101, a gadget had to be something you could hold in your hands, mechanical or electronic, and a mass-produced personal item. The rest was up to the judges. Check out their selections, and watch the 101 Gadgets TV special on History, premiering June 15. See this list HERE.