Elderly? Enfeebled? Just plain clumsy? Tokyo-based Prop has your back. Its newly announced personal, wearable airbag looks like a cool fanny-pack and weighs a mere 1.1 kilograms (2.4 pounds) -- but springs forth in one-tenth of a second when sensors detect you're headed for the floor, protecting your head and ass with two inflated bags that contain 3.9 gallons of gas each. Similar to the various airbag-equipped suits already used by some motorcyclists, the airbag is yours for a cool ¥148,000 ($1,400). Or you could just not fall down.