Recently I was reading a story and felt pulled into it from the fist page. For the most part, the story was logical and much of the police dialog was accurate. Then on the second to last page, the author caused me to hit a reading road block.
The protagonist had solved the case and was now sitting outside his home contemplating suicide. Beer in one hand Glock in the other this character was described as thumbing the safety on and off repeatedly.
Unfortunately, police issued Glocks are not equipped with an external safety. Not the kind that can be thumbed on and off. There are other police firearms with an external safety, but not the Glock.
The below photo shows a safety, which is also a decocking level found on some handguns.

This decocking level is important as weapons with them have an external hammer. If you look at a Glock the back of the gun is flat, no visible hammer hanging off the rear.
While a Glock does not have a safety to thumb on and off the weapon does still have multiple safety features, called the “safe action.” On the trigger is an extra bit of hinged plastic that needs to be depressed for the trigger to get pulled. Inside the weapon is a system of levers that only move with the trigger. These safety features make it so the weapon can only go off when a hand is on the gun and finger fully on the trigger. It is highly unlikely to make a Glock fire if it is bumped or dropped.
The lack of a safety to switch off with the thumb and safe action system made the Glock popular with police. Glock sold the weapon due to eliminating errors humans made in stress like forgetting to click off a safety. An officer can draw and fire with no other movements needed.
So if you are writing a story about firearms make sure to look at the nuances of what one firearm has for options versus another one.