The more popular alternative for police use was the Smith and Wesson Model 39 semi-auto pistol. It incorporated safety features that had already been available on other pistols, such as the double action/single action (DA/SA) trigger operation of the Walther semi-auto pistols and the magazine disconnect safety that was in use on the Browning Hi-Power. It also had a manual thumb safety, but it was mounted on the slide instead of on the frame, like the Colt or the Browning. This also served as the de-cock lever, allowing the hammer to be lowered safely on a loaded chamber, leaving the pistol in double action firing mode. It could be carried either with the safety on, which meant that the shooter's thumb would have to deactivate the safety prior to shooting the gun, or the safety could be left off and the first shot would be very similar to the familiar feel of a revolver. After that first round, however, the pistol remained in single action mode for any additional shots, unless and until the shooter intentionally lowered the hammer with the safety/decock lever. Things were getting more complicated.
Before I wrap up this history segment, the Browning Hi-Power deserves a brief digression. It was a superb single-action-only pistol, also designed to be carried cocked-and-locked. But, unlike the earlier Browning-designed Colt, it had no grip safety. As mentioned above, it did have a magazine disconnect safety, which means that the gun would not fire when the magazine was removed, even with a live round in the chamber. It also had one other feature that would dramatically influence police firearms design in the years to come: a higher capacity magazine. The Hi-Power, being a 9mm, had 14 rounds (13+1) in a gun with a very comfortable grip. The Belgian-produced Hi-Power became wildly successful in other parts of the world. Indeed, it is still in service in many places today but it never really caught on here in the States. However, it did influence how we viewed both safety features and capacity, so it deserves mention here for the purposes of our safety discussion.
This is certainly not a comprehensive history of police firearms, but I'm just trying to set the stage to review the different approaches to mechanical handgun safeties. As we discuss them in future segments, it should be helpful to understand how they came into service on police sidearms and why some people cling to the idea that the mere presence of one or more safety devices means that a gun is somehow inherently safe. Actually, all guns used in police service are inherently safe... until someone starts handling them. Then, once again, things become more complicated.