Kwikset has made a new lock it's calling Kevo that makes use of your iPhone to lose your keys for good. The idea on this one seems great, and apparently the company picked up some money from a pitch on the Shark Tank TV show. The lock has both standard key-based and wireless mechanisms, so instead of using your key, you can simply put your smartphone or a branded fob up to the lock, and it'll open up for you.
You can also send a key to someone else's smartphone, so if they need to get in your house for some reason, you can send them a temporary key that only works for a given amount of time. That's great, and because the lock is still a standard mechanical lock, it'll work like a traditional lock as well if all else fails.
The Kevo lock runs on two AA batteries for about a year, at which point those need to be replaced. Still, I'd love to have one on my apartment door. It's set to be available this summer.