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Is it safe to travel with your phone right now?
(www.theverge.com)
This is a most excellent place for technology news and articles.
On iOS, hold down power and volume up (like you’re going to power down or go into emergency mode) then cancel. Next unlock will require your PIN.
Another way on iOS is pressing the Power button 5 times. Same result, but I think it can be accomplished a little easier.
This can also call Emergency Services if you have it set up.