— -- It used to be that only locksmiths used bump keys -– a modified key that can be used to open many kinds of locks –- but now anyone can buy them online, and police are worried because the keys are increasingly being used in burglaries across the country.
In some cases people don't even know they've been burglarized. That’s because bump keys can be used to break into your house without leaving a trace.
"'GMA' on the Lookout" investigated the trend: Surveillance video of one incident in March shows two people fleeing with armfuls of property they had taken from Jacquie Diaz’s home in Sacramento, California. She initially had no idea that the theft had occurred until she noticed that some of her belongings, including an Apple laptop, were missing.
"We just couldn't figure it out, then the detective informed us, this lovely bump key," she said.
The suspects in that case were arrested and charged with burglary, but other cases of suspected bump key burglaries have popped up in other parts of the country, including Florida, Texas, Virginia and New Jersey.
A rash of 10 burglaries at an apartment complex in Marlton, New Jersey, in 2014 had investigators stumped until an expert locksmith examined one of the victim's locks.
"We focused all of our energy and investigative efforts on maintenance staff and people that would have keys...until we got told by the locksmith that this existed," Evesham Township Police Det. Gary Borbidge told ABC News.
A suspect has been charged in that case, the outcome of which is still pending.
Searching on YouTube, Det. Borbidge found hundreds of videos showing people how to make, buy and use a bump key.
Using the key effectively doesn't take much skill, only practice. Tapping -- or bumping -- the key while it's inserted into the lock causes the lock pins to jump, and the lock opens when it's turned.
The ease and availability of bump keys prompted David Rible to act.
Rible is a former Wall Township Police Department detective and certified locksmith who is now a New Jersey lawmaker. Earlier this year the state assemblyman introduced legislation that would make it a crime for anyone other than a locksmith to make, buy or own a bump key.
In a controlled environment, Rible demonstrated the ease of opening a door with a bump key for ABC News' Gio Benitez, getting a lock opened in just seconds. "The other point too is, once they're done they lock back up and leave. The homeowner comes home the door is still locked," Rible said.
A New Jersey couple -- Cathy and Art -- let Rible try opening the lock at their home ("Good Morning America" chose not to use their last name to protect their privacy). "GMA" ordered bump keys online for use in its demonstration. An entire set of bump keys -– containing 20 keys for locks from a variety of manufacturers –- cost $50.
When Rible successfully opens the lock in seconds, Cathy is shocked.
"I'm not happy because I thought they were good locks," she said. "When we put the door in we wanted really good locks for safety reasons."
After the experiment, "GMA" had a locksmith put bump-proof locks on the couple's home.
Another expert says even good locks can be bumped, which is why he wants a law that would ban the bump key. For now, he recommends investing in a high-quality bump-proof lock, such as several locks made by Medeco and Mul-T-Lock.