Smart Coasters Differentiate Iced Tea from HotWe know that you
probably don't need help figuring out if what you're drinking is
hot or cold, but that only makes these Smart Coasters all the
more endearing. Essentially a solar cell trapped in waterproof
resin, cold drinks light up blue and hot drinks light up red.
Full instructions to build your own can be found in The Hungry
Scientist Handbook (which runs about $12 at Amazon). But for the
less labor-inclined, sticking your finger into visitors' drinks
has always been considered a fine gesture of hospitality. [Evil
Mad Scientist Lab via boingboing]