A combination of a coat pistol and a blade, the dagger pistol can be used as both weapons.
The awkwardness of the configuration means you do not gain the bonus on Sleight of Hand checks that either of those stand-alone weapons grants. The dagger pistol is considered a double weapon for the purpose of creating masterwork or magical versions of this weapon. If this firearm gains the broken condition, both the firearm component and the dagger component are considered broken. A dagger pistol uses either a bullet and a single dose of black powder or an alchemical cartridge as ammunition.