A method of locating a mobile device (25) registered to a home telecommunications network (11), the method comprising: monitoring (40) network transactions; identifying (42) a first type of network transaction (30) indicating that the mobile device (25) is connected to a component of a foreign telecommunications network; identifying (44) a second type of network transaction (30) indicating that the mobile device (25) has cancelled a connection to the component of the foreign telecommunications network; locating (46) the mobile device (25) on the basis of the identified first and second types of network transaction (30); wherein locating (46) the mobile device (25) comprises setting the location status of the mobile device (25) as: within the foreign telecommunications network (29) if a network transaction of the first type has been identified, and; within the home telecommunications network (11) if a network transaction of the second type has been identified and no further network transactions of the first type have been identified.