A $300,000 watch? Luxury. A $300,000 watch that doesn't tell time -- and that sells out? Pure genius.

According to several news reports flagged by my friends at Luxist, Swiss watchmaker Romain Jerome just launched the "Day&Night" watch. The watch won't tell you what time it is. That's so yesterday. But it does tell you whether it's day or night -- helpful, I guess, for billionaire types who can't afford windows.

The...