In some implementations, radio access technology (RAT) signals can be monitored and used to synchronize an internal clock of a mobile device to a network system clock without registering the mobile device to the network. In some implementations, a RAT processor can be configured to receive RAT signals and to prevent transmission of RAT signals. In some implementations, the internal clock can be associated with a GNSS processor and can be used to calculate a location of the mobile device. In some implementations, a RAT processor that is configured for a particular radio access technology can be configured to monitor signals associated with another radio access technology when synchronizing the internal clock. In some implementations, the RAT processor can monitor signals in response to a power event. The power event can be associated with powering a display of the mobile device.