Chichester Police are urging drivers to be vigilant following 70 reported break-ins to cars and vans from across the district since the beginning of the year.
Offenders have been visiting beauty spot car parks during the day and smashing windows to gain entry to the vehicles as well as causing damage to locks and doors, according to police.
Various items such as handbags, laptops, hair straighteners and even a birthday cake have been stolen, police added.
Chidham Lane, Kingley Vale, Cocking Hill and South Harting car parks amongst others have been targeted.
Sergeant Chris White said: “We are increasing our patrols of the area at various different times of the day, but there are some things that visitors can do to help deter thieves.
“The best advice is to not leave anything of value in your vehicle, especially not on display.
“In the unfortunate event that you do return to your car and find that it has been broken in to, please make sure you report it as soon as possible through our website or by calling 101.
“In an emergency you can always call 999.”
You can report information online by visiting https://sussex.police.uk/contact-us/response-to-appeal/