A wireless communications device connected to a service network with a synchronized timing pattern therebetween is provided. In the wireless communications device, a wireless modem is configured to enable wireless signal transceiving from and to the service network in a non-sleep mode and disable wireless signal transceiving from and to the service network in a sleep mode. Also in the wireless communications device, a synchronization module is configured to initialize a first counter with a current time in the synchronized timing pattern in response to a first signal triggering the wireless modem to enter the sleep mode from the non-sleep mode, and enable counting of the first counter in a low-rate clock for the sleep mode. The synchronization module further provides the counted value of the first counter to the wireless modem to resynchronize with the service network in response to a second signal triggering the wireless modem to recover from the sleep mode to the non-sleep mode.