The warning comes in a list of crime prevention tips released by Derbyshire police following thefts in the county.
A Derbyshire police spokesman said: "With the summer months fast approaching, many people may be booking their holidays, relaxing in the garden or taking trips out in the car.
"Officers would like to take this opportunity to encourage residents to still be on their guard while enjoying themselves by taking the following simple steps to protect their property from thieves."
It only takes a moment for a thief to try a door handle and take your valuables. Ensure that windows and doors are locked when leaving the house, going up to bed or sat outside in the garden;
Keep valuable items including computers, laptops and car keys out of view and ensure they are kept away from easy access via doors, windows and letterboxes;
Mark valuable property with a UV pen so that if it is stolen and recovered by the police it can be reunited with its rightful owner;
Be a good neighbour and keep an eye on nearby properties, paying attention to any alarm sounds. Report suspicious activity to police as it happens to help stop a crime from happening;
Make sure that gardening tools and equipment are security marked and stored securely inside a shed or garage with a good-quality padlock when not in use;
Consider investing in gravel to use on footpaths and driveways leading to your property so you can hear if someone is approaching;
Use motion sensitive, infrared lighting outside your property so that lights come on to alert you if someone is close.
Going on holiday?
Make sure it looks like someone is at home by setting automatic timer switches for lights, the radio or television;
Organise for a neighbour, friend or relative to look after your house;
Cancel milk and newspaper deliveries;
Hide valuable items and lock garages and outbuildings;
Avoid putting your plans on social media or discussing travel plans where strangers may overhear about your absence from home;
On your journey avoid displaying your name and address on your luggage. Put your address inside the case to help identification if the luggage is lost.
Derbyshire is a beautiful place full of great walks but thefts often rise during the summer months. Thieves are opportunists and will only target a car if they think there is something to gain so always take a moment to think about your security;
Before leaving your vehicle unattended, ensure that it is properly secure with the windows up and the alarm activated;
Wipe away any visible marks left behind by a phone cradle or sat nav;
Remember, what isn’t there cannot be taken. Where possible, try to remove all valuable items out of the vehicle completely and if this isn’t possible always keep them out of view from passers-by. This includes wallets, bags and even loose change.