For safety purposes, Colt Single Action Army revolvers and their clones leave hammers down on empty chambers. Their safety - that is, ability to be handled safely when hammers are cocked and will fall on chambered cartridge - is significantly lower unless the user pays closer attention to the revolver.
Modern single action, single action/double action, and double action only revolvers are significantly safer to handle because their hammers will not fall on a chambered cartridge unless trigger manipulation causes it to happen. This designed feature is 100 percent reliable unless solid steel parts fail that prevent primer of chambered cartridge from being struck by firing pin. The hammer may fall or be jarred off full cock, but hammer fall will not hit the primer of cartridge in chamber. And such parts failures I have never seen, heard of, or read about. I am not referring to human error, rather to mechanisms' designs only. The only modern exception to such designed safety in modern revolvers of which I am aware is Freedom Arms Model 83.
Are similarly effective safety designs universal for semiautomatic pistols that have been designed within the past 75 years? I refer to pistols using hammers and those using strikers. And I refer to these pistols having hammers or strikers cocked over live cartridge in chamber.