The common trigger lock is just plain dangerous on a revolver. You can still release the cylinder and load it with the lock in place. Versions with an exposed hammer can have the hammer cocked with the lock in place. Again, with a little care, you can pull the entire lock assembly rearward to pull the trigger. It's a dangerous and stupid thing to do, but entirely possible. The right way to lock a revolver is to open the cylinder and put a padlock around the backstrap. It is them impossible to fire. A semi-auto should have the mag removed and the lock shackle pushed from the breech end of the magazine through the grip. That prevents the bolt from closing. Again, that prevents firing. The previously mentioned means of locking are intended only if you really don't want the firearm to be loaded and fired.
I chose a 5 button safe to keep my loaded firearms arms secured and still quickly accessible.
"A semi-auto should have the mag removed and the lock shackle pushed from the breech end of the magazine through the grip"My H&K USP Tactical has a factory locking system where you can use a specially made key that comes with the pistol that you can use to turn a lock inside the grip that prevents the trigger and hammer from moving AT ALL. Just a turn of the key literally locks the weapon. Grant it, in a self defense scenario having to remove the magazine, find the key, turn the lock, and replace the mag/chamber a round would take far too much time to protect yourself from an intruder.