DENVER (CBS4) – The Denver Police Department has a warning for anyone living in apartment complexes or high-rise lofts, especially in the northwest side of town. If you let someone in with your garage opener or key fob, it could cost you.

Officers call the thefts that come after someone is fobbed into a garage or apartment building “piggyback” crimes. They’re on the rise, according to DPD.

A mother of two, Marisha Menlove, is a little more cautious about everything these days, especially when entering her loft in Auraria.

“I don’t let them in,” Menlove said. “They have a way to call their friend and the friend can come and buzz them in, and I never let somebody in the garage.”

Last week, Menlove and her neighbors learned that the hard way, after someone came in through the garage door. Eventually, they raided cars and stole a tent from Menlove’s storage locker.

“My neighbors lost computers. Their cars were broken, crowbars broke their car windows, a lot of vandalism. It’s awful,” she said.

Since January, Denver police officers have investigated 12 “piggyback” thefts at primarily four garages and high-end complexes in Auraria and northwest Denver.

“The way to curb this is you are provided a fob for the safety of you and your residents so only you can enter or those that are allowed to enter are there,” said Jeff Martinez, Commander of Denver Police’s District 1.

According to Martinez, police have made several arrests, but the people often do it again when released or out on bond.

“A lot of them have drug problems. So, what they’re doing is finding these items they can sell quickly, and they are selling them to other people on the street, or they have a fence, somebody who can sell it cheaply and then they sell it,” Martinez said. “They’re using it to resupply their meth or heroin.”

It’s an unfortunate, yet preventable situation, and important lesson for anyone thinking they’re doing the nice, neighborly thing.

“Somebody with a backpack and a nice smile doesn’t mean they’re safe,” said Menlove.

Police say when it comes to entering garages, come all the way through and wait until the garage door starts to come down before moving forward.

“You are better to your neighbors by securing their property by making sure they have the right to enter there using their own fob,” Martinez said.