Millions of people are putting themselves at risk of things like fraud, identity theft and burglary by not using a pin code password on their phone, it's claimed.
Recent police figures suggest hundreds of mobiles are stolen every day.
Senior officers say only a fifth of people use pin codes to lock their phones. The rest are worth more money to thieves because people's personal details can be sold on.
DCI Bob Mahoney heads up the National Mobile Phone Crime Unit and gives some tips on keeping your phone safe.