Any alarm system which is installed or connected on or after the date this article becomes effective and which, when activated, generates an audible sound on the exterior of the structure being protected, shall have as part of the alarm system an automatic shutoff device, which terminates the audible portion of the alarm within fifteen minutes of the initial activation. Any alarm system which has been installed and is in operation prior to the date this article becomes effective and which, when activated, generates an audible sound on the exterior of the structure being protected, shall have an automatic shutoff device, as described above. Said device shall be installed and in operation within thirty days after the effective date of this article. (Ord. No. 1188, § 2 (part).)