Knife as a back up weapon: limitations & suggestions
Almost every officer carries a knife as both a back up weapon and as a tool for daily use. For most officers this is usually a manual (thumb flip), automatic or assisted opening clip knife that is carried in the strong side front pocket. While this is fine for a tool it has some limitations for a back up weapon.
First, if you are in a fight and cannot access your handgun it is unlikely that you will be able to access a knife in the pocket next to your holster. The exception to this is if your handgun has been dropped or knocked away.