Obvious idea: Peril Sensitive Glasses [1] that go opaque at the first sign of danger http://en.wikipedia.org/wiki/Technology_in_The_Hitchhikers_Guide_to_the_Ga

Obvious idea: Peril Sensitive Glasses [1] that go opaque at the first sign of danger http://en.wikipedia.org/wiki/Technology_in_The_Hitchhikers_Guide_to_the_Galaxy#Joo_Janta_200_Super-Chromatic_Peril_Sensitive_Sunglasses http://en.wikipedia.org/wiki/Technology_in_The_Hitchhikers_G... (Edit: HN is stripping apostrophe in link - should be Hitchhiker's_Guide)