at 7 v for the case of 9 v battery types and 9 v for the case of 12 v battery types for example transistors q 7 and q 8 cooperate with q 6 to generate a low battery voltage control signal at the collector terminal of q 8 said signal assuming a low voltage first value alarm inhibit state when voltage v br is greater than the gate threshold voltage of q 6 corresponding to acceptable battery voltage and a high voltage second value alarm enable state when v br is lower than the gate threshold voltage of q 6 corresponding to low battery voltage and indicating the need for battery replacement the control signal thus generated acts to inhibit or enable audio visual alarm circuit means 112 and audio visual indicators 16 and p 1 the low battery voltage audio visual alarm thus generated being different and distinct from that associated with a loss of telephone service with continued reference to fig3 there is illustrated a preferred circuit embodiment of audio visual alarm circuit means 112 quad dual input nand gate ic u 1 is configured as two gated astable oscillators a first modulation oscillator configured around ic gate u 1 a and a second audio oscillator configured around ic gates u 1 b u 1 c and u 1 d first modulation oscillator further comprises input components d 8 d 9 and r 16 timing components d 10 r 17 and c 8 control components.