Glock switch

A Glock switch or Glock auto-sear (sometimes called a button or a giggle switch)  is a small device that can be attached to the rear of the slide of a Glock handgun, converting the semi-automatic pistol into a selective fire machine pistol capable of fully automatic fire. As a type of auto sear, it functions by applying force to the trigger bar to prevent it from limiting fire to one round of ammunition per trigger pull. This device by itself, regardless if it is installed on a slide or not, is considered by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) to be a machine gun, making possession of the device illegal in the United States under most circumstances.

Operation
A Glock switch functions by applying force to a semi-automatic pistol's trigger bar to prevent it from limiting fire to one round of ammunition per trigger pull. Normally, in a semiautomatic pistol, after firing, the trigger bar catches the firing pin until the trigger is released, but when depressed by the switch it does not catch. A Glock switch thus converts the weapon into a machine pistol capable of automatic fire. The device is roughly the size of a United States quarter, and when installed on the rear of the slide on a Glock pistol (replacing the slide cover plate), adds a selective fire switch; flipping the switch sets the weapon to full automatic mode, which is capable of firing at a theoretical cyclic rate of 1,000-1,400 rounds per minute.

History
A patent for the Glock auto-sear was filed in 1996 and approved in 1998, with its invention credited to Venezuelan Jorge A. Leon, who claims to have invented the device in 1987.

The first reported appearance of Glock switches in the United States occurred in 2002 when an Argentinian was arrested for sending Glock Switches among other illegal firearms to the United States, with 16 later being recovered by the ATF in 2003.

A handgun with a Glock switch attached fits the definition of a machine gun under United States federal law. The 1986 Firearm Owners Protection Act made new machine guns illegal for civilians to own, banning "possession and transfer of new automatic firearms and parts that fire bullets without stopping once the trigger is depressed", with the exception of machine guns manufactured prior to May 19, 1986. The penalties for possession of an unregistered machine gun in the United States are up to a $250,000 fine and prison sentences of up to 10 years.

In 2019, the ATF recovered thousands of the devices which were imported from China. In 2021 and 2022, people have been manufacturing the switch devices with 3D printers. In March 2022, a Vice News investigation learned that the federal prosecutions which involved conversion devices have been rising since 2017. They determined that from 2017 to 2022, advances in low-cost 3D printers and global commerce on the internet have made the devices available for as little as US$20. In 2022, federal authorities documented a dramatic rise in the prevalence of the Glock switches.