From GadgetHacks: Your Pixel Has a Hidden QR Code Reader — Here's How to Use It
Open the default Camera app. Direct the camera app towards a QR code. You will see a small popup just above the shutter button with a preview of the QR code results. Tap on the popup, in our case it's a Wiki link. When you do, you will be directed to the specific location of the QR code, be it a website or a deep link within an app.