SPRINGFIELD, Mass. (WWLP) – Springfield Police have a warning about a dangerous attachment they’re seeing on guns.

When using a semi-automatic pistol, one pull of the trigger shoots one bullet. But a small, coin-sized device that can be attached to a gun called a Glock switch turns it into an automatic weapon.

A Glock switch attached to a gun that was seized by Springfield Police in January.

“It interrupts the normal cycle of fire, so you pull the trigger once and hold it down, and it will spray until you stop, continuously fire until you stop,” explained Capt. Brian Keenan of the Springfield Police Department.

Capt. Keenan told the 22News I-Team they have been seeing these more and more on the streets. He said there were 24 Glock switches seized in Springfield in the past year.

“A Glock switch will make a semiautomatic pistol or rifle that much more deadly,” said Keenan. “The amount of rounds you’re able to extract from the gun so quickly are inherently dangerous. Glock switches serve no legitimate purpose in the firearm world.”

Glock switches aren’t sold in firearms stores. They are illegal aftermarket add-ons that have to be ordered online, usually from China. Glock does not make them.

“When police officers and military people are taught to shoot, they select a target and pull the trigger,” Keenan explains. “With these devices, you’re just pulling the trigger and letting the rounds fly.”

Using a Glock switch is a federal crime because they’re considered machine guns, which are illegal according to the US Alcohol Tobacco & Firearms (ATF). State Sen. John Velis is planning to file new legislation that would ban switches at the state level.

Glock Switch (US Alcohol Tobacco & Firearms)

“These devices exist for no reason, but quite frankly, to kill people. The ATF and other agencies, they’ve got limited resources,” Velis said. “Equipping local law enforcement to take these devices off the streets is really, really needed right now. Why not give them the mechanism to take that off the street?”

Glock switches are also sometimes referred to as “sear selector switches.” Under federal law, a person can be sentenced to up to 10 years in prison for possessing a gun with a switch.