A Weapon with a double trigger treats one trigger as a “safety,” with the second trigger being a hair trigger that fires when the slightest pressure is applied to it. Weapons of this type can be extremely accurate, since only a small amount of pressure is needed to fire them (reducing the chance of moving the weapon slightly while pulling the trigger), but this takes time and training. If a character has the Careful Shot feat, they gain a +2 bonus on attack rolls if he aims with a weapon that has the double trigger (rather than the normal +1 bonus provided by the feat).

Source: Scum and Villainy, p. 43