In general, the invention provides a method for detecing a bad RF state, and saving battery power by entering different sleep mode levels or stages according to the RF state. When a mobile device detects the bad RF state and enters a deep sleep opertion mode, the life time of the battery of the mobile device can be kept. In the deep sleep opertion mode, the mobile device periodically samples the RF state, when the RF state is not improved, time intervals between samples are gradually increased. Because even in a good RF coverage region, the movability can changes the RF state of a wireless device, the mobile device operated in the deep sleep mode is able to detect the movability and increase the possibility of entering an idle state, or slectively, entering a longer power saving mode. When the RF state is improved, the mobile device exits from the deep sleep mode, and returns the idle state.