Waiting on hold

IN THE battle against Ebola, mobile phones could be invaluable—not just in themselves, as devices that can be used to send people public-health information or let them call helplines, but also because of the data they generate. Phone companies use call-data records, or CDRs, to manage their networks and bill their customers. These records include a caller’s identity, the time of the call, the phone tower that handled it and the number called. Other data which the firms collect can identify where a phone is even if it is not being used, because phones constantly send out signals so that their location is known, to enable them to receive calls.

CDRs can therefore tell epidemiologists where people have been, when—and perhaps also where they are headed, based on their past movements. Analysing the records has proved helpful in tracking the spread of diseases on previous occasions.