(WXYZ) — It's commonly called a "Glock switch," but Detroit police call it a nightmare because the quarter-size device can turn a semiautomatic handgun into a fully automatic weapon.
"The mindset is to inflict as much damage as they can as quickly as possible," said Detroit Police Commander Ryan Connor.
On the city's west side, Kevin Miller manages a barber shop and says it's unsettling the number of young people he sees walking around with firearms.
"They're walking around, it's like watching an old western, they have some big guns with long clips. What do you need all that for?" said Miller.
VIDEO: Watch an ATF agent demonstrate how a Glock switch changes the weapon's firing:
"They're illegal. You can't possess them, and they turn a regular handgun into almost a machine-style weapon," said Captain Marcus Thirlkill of the Detroit Police Department.
A "Glock switch" is also classified as a machine gun under federal law, according to The Bureau of Alcohol, Tobacco, and Firearms (ATF).
Commander Connor and Captain Thirlkill lead the organized crime division for the Detroit Police Department— and they're seeing a growing number of criminals using these machine-gun conversion devices.
"Year to date, we've recovered approximately 50 'Glock switches' off the street, and half of those have been used in violent crime," said Commander Connor.
Investigators say criminals are buying them online or simply making them at home with 3D printers.
"That's dangerous. We're not at war ... why you need a gun like that in the first place ... it's scary for one thing," said Constance Barnes, who lives on Detroit's west side.
It's important to note that "Glock switches" are often used on Glock pistols, but they are not made by the gunmaker. They were invented by Jorge Leon, who said he wanted to help the military and police. He now calls his invention a catastrophe.
"The biggest problem and the nightmare for law enforcement is large capacity crowds ... the amount of victims that it can cause versus, what's legal is a semi-automatic handgun," said Commander Connor.
After Sunday's mass shooting at an illegal block party on Rossini Street, police recovered multiple firearms, including one 'Glock switch."
Twenty-one people were shot on Rossini. A man and a woman died from their injuries.
"You've fired a fully automatic ... can you imagine firing a fully auto out of a handgun?" said Terry Johnson, attorney and gun rights advocate.
Attorney Terry Johnson has experienced the power of a fully automatic firearm. He's a gun rights advocate who says this about Jorge Leon's invention: "the Glock switch is very dangerous for the public."
He added, "No one is trained to use a handgun that's fully automatic. And there's a reason for that."
And that's why Detroit police are sending the message — if you're caught just in possession of a 'Glock switch' or making them, you can bank on being prosecuted federally.
"To hear machine-style weapon, and in a neighborhood where houses are in close proximity together is frightening," said Captain Thirlkill.
So if you have information on anyone involved in making or possessing a Glock switch, you're urged to call Crime Stoppers at 1-800-SPEAK-UP or Detroit Rewards TV.
"It's scary ... something like that can turn a weapon into a killing machine," said Miller.
Johnson said this is not an anti-Second Amendment discussion, but that it's about safety.
"If these ('Glock switches') were such a good idea, they would be in gun stores everywhere. There's a reason that they're not. They're illegal, they're dangerous, and they're harmful," Johnson said.
"We will find you, we will arrest you, and we will prosecute you," said Commander Connor.
