Hikers are being urged not to leave valuables in their cars near Thame beauty spots following a spate of thefts.
Ten cars have been broken into and items stolen since the start of January.
Area beat officer Graham Martin said he thought thieves may have been lying in wait for people to leave their cars for long periods while off walking.
He said: "People think this type of crime only happens in the summer but it's a problem we face all year round.
"People often visit places like Christmas Common after they have been shopping and leave a large amount of goods in their cars.
"It only takes a second for an offender to smash and grab. Be safe.
"Take your valuables with you or leave them at home." Pc Martin issued the following advice:
Park your car in a position where it can be easily seen
Do not try and hide the items under car seats or in the boot
Make sure the vehicle is locked and the windows are shut
Look out for anyone suspicious and try to make a note of their car number plate
Anyone with information about the thefts should call 08458 505505 or Crimestoppers on 0800 555111.
For more information about car security, call 01844 264945.
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