[Secret Agent Man]

Needs a good shotgun. Crooks instinctively fear the ‘clik-clak’ of a shotshell being chambered.

[AnAmericanMother]

Oh, yeah. That "ka-CHUNK!" sound of the bolt slamming home into the receiver with a shell seems to penetrate the brain of even the slowest of thieves.

Friend of mine who was a local police officer used to recommend to the little old ladies who asked what gun they should get to get a pump shotgun -- "you don't even need any ammo. Just rack it, and if you don't hear breaking glass and beating feet there was never anybody there in the first place."