Everyone knows the ol' key-under-the-rock trick for hiding your spare keys for guests, but it's not exactly a secure method. Still, sometimes it's preferable to the scheduling nightmare of arranging when and where to hand them off. Not so if Hoard has its way, however. Describing itself as a local drop box, Hoard is essentially like Amazon's delivery lockers, except for your own stuff. Here's how it works: You use the app to find the closest "hoard spot" to you and get the code for a tiny locker box, as seen above. You deposit the keys in the appropriate locale, send a confirmation to your guest, and then he or she will use the same code to retrieve them (bearing in mind the code is only good for 48 hours). They can also use the same method to hand the keys back to you.