Methdo and system of wireless device power management

A wireless device comprising:

• a first circuit configured to perform normal operation of the wireless device in a normal operation mode and configured to be powered down in a power-down standby (PDS) mode, the first circuit at least including a processor and a memory coupled to the processor for storing program instructions and data;
• a second circuit at least including a low-power processor, a built-in battery, and an event detector, and configured to perform a power management function including:
• in response to detecting a wake-up event by the event detector, changing the first circuit from the PDS mode to the normal operation mode;
• and
• in response to detecting a PDS event by the event detector, changing the first circuit from the normal operation mode to the PDS mode;
• a power source;
• and
• a switch configured between the first circuit and the power source and controlled by the second circuit to connect the first circuit to the power source or disconnect the first circuit from the power source,
• wherein the first circuit and the second circuit are independent of each other, the first circuit operates without relying on any component of the second circuit, and the second circuit operates without relying on any component of the first circuit.