A display device includes a dial, an alarm setting member, and a warning unit. The alarm setting member includes an A/D converter, a recognition module, a storage module, and an analysis module. With rotation of the dial, a variation voltage is generated. The A/D converter converts variable voltage from analog to digital form. In contrast, the alarm time is decreased. The storage module stores the adjusted alarm time. The analysis module compares the current time with the preset alarm time and outputs a driving signal to the warning unit in the event of a match.