By Karen Anderson, WBZ-TV

BOSTON (CBS) – You think you’re safely locked in your home when you secure your dead bolt, but there could be a dangerous problem in your door.

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The I-Team discovered if your dead bolt isn’t properly installed, burglars may be able to get in without any trouble.

Chris Kiertz and his girlfriend Alex thought they were secure, but when they were locked inside, someone was trying to break into their Brookline home. Chris says he turned the doorknob, and heard two people bolt down the stairs.

They scared the burglars off, but another woman who asked not to be identified, was not so lucky.

After thieves broke into her home, she had her locks checked and discovered the dead bolt was not properly installed.

The pocket that the bolt slides into wasn’t deep enough, and so burglars were easily able to pry it open with a putty knife.

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We asked Mike McCarthy from ProGlass and Lock in Newton to show us how it works.

He says if a bolt isn’t fully extended, it’s not dead locked. If the dead bolt isn’t able to be fully opened, than it can easily be pried right back into the door.

McCarthy says he sees many cases of problems. “It’s very simple. The putty knife will slide that right back into the door, and the door is unlocked again.”

Boston Police Officer Izzy Marrero helps check people’s homes to make sure they are secure, and says he finds a lot of homes with dead bolts that are not properly installed.

He encourages people to check their locks, or have a police or a professional check them.

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We showed Chris and Alex, and Chris said, “You never think about it’s until it happens.” It’s a simple check to keep you safe.