The .40 S&W or .40 Smith & Wesson cartridge is a popular and relatively new round designed primarily as a more effective replacement for the 9mm round, which has been shown to lack sufficient stopping power according to some studies and real world events including FBI related shootings.
Appeal for Home Security
The .40 S&W is popular for home security for several reasons. The first is that it offers greater stopping power than the 9mm, while maintaining more manageable recoil and a lower price per round than the .45 ACP. The second is that it is the standard issue round for many law enforcement agencies in the United States.