Thieves targeted over 50 work vans in Cardiff and the Vale last month, according to South Wales Police.
Barry was the worst affected area in the region, followed by the Fairwater area of Cardiff.
It's believed the suspects have been mostly targeting the vehicles for power tools.
Detectives say they're investigating the recent spate of thefts and are reminding van owners to be on their guard.
A spokesperson for South Wales Police said: "We understand that having your van or work vehicle stolen, broken into and contents stolen can be very distressing. These recent thefts are being investigated."
"When you’re parking your van, even for short periods, please think carefully about where you are stopping. Parking with the rear or side doors against a wall or very sturdy railings will help to ensure that they can’t be prised open."
"Please consider removing tools and other items from vehicles overnight."
More security advice can be found on the Secured by Advice website.
Candlelit vigil held for White Ribbon Day
Mental health Hangout opens in Barry
Two charged with Barry Island stabbing
Mayor to host Christmas Market
Santa Sleigh returns to Barry
Barry Island: two arrests after serious assault
Tui to expand Cardiff Airport flights
Vale Council facing £14.8m budget gap
Santa's reindeer let loose in Cardiff Bay
Sculptures on show at Art Central
BA to expand Cardiff Airport maintenance base
New contractors for Ysgol Llyn Derw
Big winter party for More in Common group
Review: Array truly shine in expert retelling of Sondheim's ‘Company’
Gloves on for Barry volunteer
First look at Gavin and Stacey: The Finale, coming on Christmas Day
Barry Biomass on the brink?
Penarth walk raises funds for new gym equipment
