Brain/Mindset
A firearm with all of the typical 1911 safeties
A Glock's safe-action trigger, or similar mechanism
A firearm with one manual safety
Muscle memory from sufficient training, no thinking required
A firearm with a Bio-safety (DNA analysis, fingerprint recognition, etc.)
No safety is needed, guns and shooters are flawless without
No gun is safe, except for the one in the scrap pile
Once again:
The most important safety device resides in your head, between your ears.