A receiving module, checking module, and a controller are provided. The receiving module is configured for receiving external wireless signals. The checking module is configured for checking whether a current wireless signal comprises checking codes of a control signal which is configured for controlling the electronic device and, if yes, generating an activation signal. The controller is configured for switching the electronic device into a power-saving mode if no external wireless signal is received after a predetermined time period and switching the electronic device into a normal mode if the activation signal is received.