Methods, systems, apparatus, and non-transitory media are disclosed to perform state-based changes on a mobile computing device. A mobile computing device may display one or more images that are indicative of a state of the mobile computing device, such as a barcode. A mobile computing device may measure characteristics of electromagnetic (EM) radiation, such as laser light from a laser scanner, received through its camera. By comparing changes in the intensity of the EM radiation over a time interval and/or a wavelength of the EM radiation to one or more threshold intensities and/or wavelength ranges, one or more trigger conditions may be identified. The one or more trigger conditions may cause the mobile computing device to execute one or more actions, which may be dependent on the present state of the mobile computing device. The actions may include various functions used in conjunction with a retailer-based mobile phone application.