Many open-carry holsters have that feature.
Someone tried to comply.
Incident. Las Vegas
At 11:35 am,[17] as Trump was speaking, Sandford noticed that Ameel Jacob, a police officer with the Las Vegas Metropolitan Police Department who was providing security for the event, appeared to have his 9mm Glock 17 pistol unlocked in its holster.
Sandford approached Jacob, who was positioned approximately nine meters (30 feet) from the stage where Trump was speaking, and engaged him in conversation, saying that he wanted Trump's autograph. While talking to Jacob, Sandford "reached down to try and pull the officer's gun, but it got stuck in his holster".[2][12]
Sandford was immediately subdued and arrested by Jacob and two other police officers.[13][18][19] Sandford was described as appearing "confused" at the time of his arrest.[20][21] Police officers are widely equipped with retention holsters that prevent their firearm from unlocking until a release mechanism has been engaged.
In many cases, there are additional retention devices in use other than the typical leather strap or rotating hood that cover the top of the handgun.[citation needed]
Many open-carry holsters have that feature.