From GSM mobile system if you dial 112 then that call diverted to the assigned emergency center. In India call diverted to local police station, in North America the call is diverted to 911.
112 can dial from cellular phone even when keypad is locked. When I was at Hyderabad I tried 112 from my locked Nokia device, the call was diverted to police station.
If you are out of your country and you are in trouble just dial 112.
Note :- Do not trust on Indian 100 number. When thieves attacked on me and I called 100 from my cell phone, the ring goes to some house in nearby city Yawal.