August Smart Lock

The puck-size anodized-aluminum August Smart Lock affixes to your existing dead bolt and augments it with a sensor: It recognizes when an approved phone is approaching and automatically unlocks (you can lock and unlock it remotely, too). It's elegant and inconspicuous, and prevents you from fumbling for your keys. What's more, you can program the lock to issue temporary "keys" that allow certain people entrance during specific hours (say, a neighbor to water your plants). If your phone is lost or stolen, no problem: You can instantly shut off access by logging onto August's website. [$199;]