Over the last week power tools were stolen from four Ford Transit vans and two cars had their catalytic convertors taken in Hitchin, Stevenage, welwyn garden city, letchworth and surrounding areas.
There were also three vans that were broken into in Letchworth during mid-February.
Between 5pm on Thursday and 6.55am on Saturday power tools were stolen from four vans on Halsey Drive, Kings Down, Tristam Road and Highover Way in Hitchin.
And between 10pm on Thursday and 11am on Friday catalytic converters were stolen from parked silver Ford Galaxy in St Michaels Road and a Seat Alhambra in Lucas Lane.
In mid-December power tools were stolen from vans in Alban Road, Fleetwood and Kyrkeby in Letchworth.
?Van drivers and owners of vehicles with catalytic convertors need to be on their guard.
?The message is clear ? don?t leave anything in your vehicle at any time and keep your vehicle secure.
Residents should keep a lookout for anyone behaving suspiciously. All of these crimes are believed to have occurred overnight.?
Anyone with information should call the police non-emergency number 101, but if you see anyone acting suspiciously you are advised to call 999.