A structure is to affix an optical plate on a frame in a panel display. The battery state monitoring circuit includes a voltage comparator circuit and a power supply voltage detection circuit for detecting an abrupt decrease in power supply voltage, in which the voltage comparator circuit detects a normal overcurrent while the power supply voltage detection circuit detects the abrupt decrease in power supply voltage caused by load short-circuit. The card reader is configured to reliably read data encoded in a magnetic strip of the card with minimum error in a single swipe and provide a signal that corresponds to the data read to the mobile device, which then decodes the incoming signal from the card reader and acts as a point-of-sale device to complete the financial transaction.