To check for a half-cock, follow the instructions in post #3, or as an alternative.
1. Field strip the pistol. When you are done the hammer should be cocked. If your pistol has the magazine disconect feature, replace the EMPTY magazine.
2. Place your weak-hand thumb over the face of the hammer, pull the trigger, and ease the hammer all of the way forward. With the hammer forward you should note that the grip safety is compressed into the frame (fire position) and the manual safety is down in the "fire" position.
3. While holding the grip safety in, use your thumb to push the hammer backwards about 1/4 inch. If there is a half-cock notch you will hear a click, and if you release the pressure on the hammer it will not return all of the down.
4. When you are finished, push the hammer back to the full-cock position, remove the magazine, and reassemble the pistol.
In normal operation the slide cocks the hammer when it is retracted, in the same way a .45 Colt pistol does, but because the hammer is enclosed you can't see it.