will sound an alarm at three o'clock this afternoon when the government tests a new emergency alert system. it'll be used to warn people about serious risks that could threaten lives, such as flooding, wildfires, and even terror attacks. dan johnson reports. loud beep brace yourself for the three o'clock alert. up and down the country this afternoon almost every smart phone will make this noise. loud beep tell me what you think? yeah, it's something different. it's a new sound coming out of your telephone. loud beep ok, it's not too bad, i thought it was going to be worse. it's not too bad. not too bad. you think that's all right? yes. do you think people will get taken by surprise? yes, for sure. so every phone in the uk