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As news of the Paris attacks spread around the world minds turned quickly to friends or family living or visiting the French capital to ask: are they safe?
Facebook has tried to replace the scramble to call, text and pass on messages across families and continents with a system that uses the facility to locate and contact a network of 1.5bn monthly active users.
When activated by the social network, Facebook Safety Alert buzzes the smartphone of anyone it thinks could be in the location of a serious attack or natural disaster, asking them to confirm ‘I’m safe’ so the message can be sent to their friends.
For those watching coverage of a disaster on live TV news or gripped to posts of witnesses online, they can rely on the app to take a register of their personal connections: Lizzie is safe, Kate is safe, Olivia is safe.
Facebook’s Safety Alert was launched last year and has been used several times. It was activated as hurricane Patricia headed towards the coast of Mexico, comforting millions of Mexican migrants around the world, and to locate survivors in the earthquakes in Afghanistan and Nepal.
The feature came out of an impromptu tool called the disaster message board created by Facebook engineers in Japan after the 2011 earthquake and tsunami.
On Friday night, Mark Zuckerberg, Facebook founder and chief executive, wrote on the site that his thoughts were with everybody in Paris. “Violence like this has no place in any city or country in the world,” he wrote as he announced the deployment of Facebook safety check.
Onlookers also turned to social media to show their solidarity with Paris and France. On Facebook they were asked if they wanted to place a Tricolore filter over their profile picture, turning it the colours of the French flag, while on Twitter and Instagram many shared a picture of a peace symbol with the Eiffel Tower at its centre.
Some 13,000 Parisians used the #porteouverte — open door — hashtag to show they were ready to welcome people shut out in the city. Outside Paris, 17,000 people used the hashtag #PrayforParis, according to data from Twitter analytics firm Topsy. There were 40,000 tweets about La Marseillaise, after the French National Assembly sung the national anthem.
Others used social media to voice their concerns about a backlash blaming all immigrants and Muslims for the attack. There were 120,000 tweets using the hashtag #Muslimsarenotterrorist, saying a religion cannot be blamed for the acts of a few.
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