Use Smart Lock Nexus 6

Smart Lock enables you to create trusted places, faces, and devices. When your phone recognizes those trusted things it will disable the lock screen. For example, you can have the lock screen disabled when your smartwatch is connected or when you’re at home. Here’s how to set up a trusted place, face, or device.

1.Go to Settings > Security > Smart Lock
2.You’ll be asked to create some sort of password, pin, or pattern lock
3.Next you will see Trusted devices, Trusted places, and Trusted face
4.In Trusted devices tap Add trusted device and then choose Bluetooth or NFC
5.Simply choose a device that is connected or tap and NFC tag
6.Trusted places will allow you to choose a place from your Google Maps locations, or use the map to create a new place
7.Trusted face will guide you through the process of scanning your face

That's nice