In the context of firearms, a safety is generally a mechanical system that prevents the gun from releasing the hammer or striker to activate the primer of a cartridge, thus expelling a projectile without a deliberate pull of the trigger. Manual safeties are generally externally mounted on firearms and display a visual representation that they are engaged or not by using etched markings or colored symbols. They must be manually disengaged and re-engaged by the user. Many modern firearms feature internal safeties which are disengaged sequentially during the process of pulling the trigger, or remain engaged to prevent the firearm from firing out of battery, or if dropped accidentally. These types of safeties will prevent the pistol from firing unless the trigger is deliberately pressed. Many firearms have internal and manual safeties. Regardless of how many and which safeties a firearm offers, properly adhering to the Four Rules of Firearm Safety should always be followed.