A book on humility. Or a pair of $350 sunglasses that go beep when you leave them behind. From the makers – who handbuild each set so give them a break over that price – comes this explanation:

Never lose your eyewear, or your phone. We embedded custom designed beacons into every pair of Tzukuris. This means your iPhone will alert you if you leave them behind and the app can show you where you left them. Using the iPhone’s motion sensor, the app recognizes if your phone is left behind and will ring extra loudly to alert you.

They’re called Tzukuri sunglasses. Read more on the official website and also at Time magazine which has more to say about them.