Multi-functional alarming system

A multi-functional alarm system comprising

• a capacitive-type microphone for sensing ambient sound and providing an output responsive thereto;
• a microphone amplifier for receiving the output from said microphone and for outputting analog signals representative of said ambient sound;
• a vocoder for receiving said analog signals and having a memory, a recording switch and a playing switch, whereby the vocoder digitalizes said analog signals and stores the digitalized signals in said memory when said recording switch is in an ON position, and whereby the vocoder retrieves any digitalized signals stored in said memory and outputs converted analog signals having positive and negative phase components when said playing switch is in an ON position;
• an audio preamplifier for receiving said converted analog signals and having two calculation amplifiers for respectively amplifying the positive and negative phase components of the converted analog signals and respectively outputting amplified positive and negative phase signals;
• a power amplifier formed as a bridge circuit for receiving said amplified phase signals, further amplifying the amplified positive phase signal by means of first and second transistors and further amplifying the amplified negative phase signal by means of third and fourth transistors, the bases of the first and second transistors each being driven by a fifth transistor, the bases of the third and fourth transistors each being driven by a sixth transistor;
• a speaker for providing audible sound when said playing switch is in said ON position;
• and
• twin variable resistors for adjusting the output power applied to the speaker.