Shared or lost keys can unlock the door to trouble. When the "key" to your house is on your phone, though, or entered into a keypad, you don't need to worry as much that others might have unlimited access to your home. Upgrading the deadbolt on your door with technology like the August Smart Lock can give you greater control over who enters your home and when. Create temporary virtual keys for guests to arrive at prearranged times, or simply buzz them in at a moment's notice from your phone. For peace of mind, you can check back on the app for a full log of recent visitors. Available on Amazon; $199.