How to set Double-tap to scan

While on the Home screen, tap twice on the sensor on the back of the phone to scan a code.

Setting method: 

Settings > Special features > Smart sensing > Double-tap to scan

How to do it:

Point the camera at a QR code and quickly tap twice on the sensor on the back of the phone to scan the code.

Note: Only some models support this function. Please refer to your actual experience.