LOCK it or Lose it, is the message from police after figures showed 36 per cent of homes burgled in April were left insecure.
Of the 76 house breaks last month, 27 were vulnerable to attack because of unlocked doors and other security flaws.
Officers in Gloucester are giving residents crime reduction advice as part of the 'Lock it' campaign and hope people will take their home security more seriously as a result.
Sergeant El Lakin said: "The problem has obviously been widespread and has meant opportunist burglars, who have become very wise to it, have simply been trying doors in a number of areas across the city until they come across an insecure door.
"Many of the burglars have got in through unlocked front doors when occupants have been in bed asleep.
"The impact can be devastating and cause huge disruption to people's lives. Insecure doors can also of course void your home insurance.
"We have been working hard to catch offenders - and have made three arrests in recent weeks - but we need people in the community to help themselves.
"The community teams really wish to get the message out to all residents to ‘Lock it’ - we need their help to make sure they routinely check doors and windows when leaving their homes and add it to their bedtime routine.
"We cannot urge you more to take these simple steps to keep homes safe and secure."
Officers will be posting advice on the Twitter hashtag #gloslockit and people are encouraged to look at the crime reduction guidance on special leaflets being distributed across the city.
More advice can be found at the crime reduction pages of www.gloucestershire.police.uk.