Daylight saving and warmer weather bring a spike in burglaries, disorder, theft of motor vehicles, thefts and assaults or street robberies.
It takes an opportunist just 10 minutes to break into your house, and the message from Whanganui police is to be vigilant now the warmer weather is here.
Acting Senior Sergeant Andrew McDonald says locals tended to open up their homes after the winter. People were also more social and out and about, with many playing twilight sports.
But so are those opportunists who see an open window as an invitation to break into your home, Mr McDonald warned.
"There are more opportunities for offenders to commit a crime when windows are left open," he said.
And while "popping out to the supermarket to pick up a couple of groceries" may seem a quick trip, it could also provide enough time for offenders to take advantage of an open window in an empty house.
Another warning from police is to not make yourself or your property an easy target.
The warmer months are when opportunists see someone who they think is vulnerable, knock them to the ground and snatch their handbags.
But it's about the public taking responsibility and keeping themselves and property safe, he says, "reducing the opportunity to become a victim".
"People should lock their cars, wind up their windows and stow any valuables out of sight."
Electronic items such as laptops, iPhones, cameras and iPads should not be left in the car or, if they are, not in view.
"Out of sight, out of mind," is the simple rule, Mr McDonald emphasises.
"This makes it harder for these opportunists to take advantage."