Google showed off the trusted device unlock support back at Google I/O, but the feature didn't make it into the last dev preview. Well, it's there now and it works as advertised. Just pair your favorite wearable or Bluetooth gizmo, and the secure lock screen goes away. Lose connection, and it's back.
In Lollipop, when you add a new Bluetooth device, a notification will ask you if you'd like to make it a "trusted device." That means if your watch, car, or whatever device is connected, you can access the device simply by swiping away the lock screen. Your PIN or pattern remains in effect, so the entire process is smooth. The same is true for NFC, but you'll need to add these tags through the smart lock menu. Select NFC, tap the tag, and now your phone will skip the secure lock screen when it's in range.
A few phones already have this feature—for example, the Moto X. However, Lollipop doesn't saddle you with a persistent trusted device notification like that device does. It's all taken care of for you with a subtle padlock icon on the lock screen to tell you what's up.