A method for alerting the authorities that a person with a gun has entered a safe zone includes the steps of: (a) downloading to an app-enabled, and GPS-enabled, smartphone the coordinates of one or more safe zones in which the unauthorized presence of guns is prohibited; (b) when said smartphone enters a safe zone, sensing the presence of any gun that is in the vicinity of said smartphone; and (c) if the presence of a gun is sensed in the vicinity of said smartphone, transmitting an alert message by means of said smartphone to a central office for the attention of security forces. Apparatus for carrying out this method includes a transponder tag attached to a gun and an app-enabled, and GPS-enabled, smartphone capable of determining when the smartphone is within a safe zone and capable of sensing the presence of the transponder tag.