Twitter, smartphones can help determine crowd size
 

Data from smartphones and Twitter can accurately show the size of a crowd, helping first responders in an emergency.Scientists at England's University of Warwick devised a computer model based on data from Twitter and from phone companies in Milan, northern Italy."Accurate estimates of the number of people in a given location at a given time can be extrapolated from mobile phone data, without requiring users to install further applications on their smartphones."