Laser scanners emit light when they scan because the laser light must be reflected back in order to read the barcode. 1D barcodes are composed of black and white bars where the space between the black and white bars define the value. Laser scanners cannot scan barcodes displayed on phone screens because light is not reflected back. Mobile phones have anti-reflection technology to prevent glare and they are constantly emitting their own light from their LCD screens.
Laser scanners also cannot read 2D barcodes, like QR codes, because of the way they’re created. QR codes are created in squares, with colored square dots indicating characters. 2D barcodes can be complex and contain lots of information, while 1D barcodes are simple and limited to a specific number of characters.