A method performed by a mobile device incorporating a cellular radio subsystem and a wireless local area network 'WAN' radio subsystem, the method comprising: over a period of time, receiving cellular signal strength measurements from the cellular radio subsystem and receiving WLAN signal strength measurements from the WLAN radio subsystem; characterised in that the method further comprises: detecting an outdoor-to-indoor transition (104, 122) for the mobile device by determining that, over the period of time, the cellular signal strength measurements have exhibited a decreasing trend and the WLAN signal strength measurements have exhibited an increasing trend; in response to detecting the outdoor-to-indoor transition, increasing a background scanning frequency of the WLAN subsystem; after increasing the background scanning frequency in response to detecting the outdoor-to-indoor transition, performing background scanning by the WLAN radio subsystem at the increased background scanning frequency; determining whether results of the background scanning match any WLAN profile saved in the mobile device; and where none of the results match any WLAN profile saved in the mobile device, gradually reducing the frequency at which background scanning by the WLAN radio subsystem is performed. over a period of time, receiving cellular signal strength measurements from the cellular radio subsystem and receiving WLAN signal strength measurements from the WLAN radio subsystem; characterised in that the method further comprises: detecting an outdoor-to-indoor transition (104, 122) for the mobile device by determining that, over the period of time, the cellular signal strength measurements have exhibited a decreasing trend and the WLAN signal strength measurements have exhibited an increasing trend; in response to detecting the outdoor-to-indoor transition, increasing a background scanning frequency of the WLAN subsystem; after increasing the background scanning frequency in response to detecting the outdoor-to-indoor transition, performing background scanning by the WLAN radio subsystem at the increased background scanning frequency; determining whether results of the background scanning match any WLAN profile saved in the mobile device; and where none of the results match any WLAN profile saved in the mobile device, gradually reducing the frequency at which background scanning by the WLAN radio subsystem is performed. detecting an outdoor-to-indoor transition (104, 122) for the mobile device by determining that, over the period of time, the cellular signal strength measurements have exhibited a decreasing trend and the WLAN signal strength measurements have exhibited an increasing trend; in response to detecting the outdoor-to-indoor transition, increasing a background scanning frequency of the WLAN subsystem; after increasing the background scanning frequency in response to detecting the outdoor-to-indoor transition, performing background scanning by the WLAN radio subsystem at the increased background scanning frequency; determining whether results of the background scanning match any WLAN profile saved in the mobile device; and where none of the results match any WLAN profile saved in the mobile device, gradually reducing the frequency at which background scanning by the WLAN radio subsystem is performed.