The Sig 4 Point Safety System -
1-De-cocking lever- Lets you safely lower the hammer with a loaded chamber.
2-Firing pin block. The firing pin cannot move forward if the trigger is not being pressed. This is also called "Drop Safety"
3-Safety Intercept Notch. The reason the hammer is not touching the firing ping when it is down, if the trigger is not pressed the hammer cannot move all the way forward.
4-Trigger bar disconnect. While the slide is cycling, the trigger bar is disconnected from the sear to avoid an out-of-battery discharge.
What it is and how it works! A long needed video explanation of how the internal and passive safeties work on the Sig Sauer P226.
This video is an excerpt from a larger comprehensive review you can find on my channel. Hope this helps to shed some light on some of the engineering that goes into a Sig.