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By the time the symptoms of highly infectious diseases such as Ebola become apparent, many people in an environment such as a hospital or military base may have been infected by the victim. The Lawrence Livermore National Laboratory and the University of California have patented a system that continually tracks all contacts between its staff (US 2003/204130). The staff carry a PDA, cellphone or pager with a WiFi connection that checks the proximity of other devices. The devices transmit the time and date of each encounter back to a central station that keeps a log of all such meetings. If anyone becomes infected, the system identifies people who have come into contact with the victim and so are at risk of becoming ill.