New wristband warns when you've been been in the sun too long

Paper bracelet printed with light sensitive ink signals UV exposure to wearer with smiley and frowny face symbols

A simple paper sensor featuring smiley and frowny faces drawn in UV-sensitive ink has been produced by researchers in a bid to keep us safe in the sun.

Scientists say the different expressions appear in sequence as UV exposure increases, offering a low-tech way for people to gauge when it is time to cover up.