A failsafe bandpass filter/decoder system comprising: an active bandpass filter which comprises a high-pass filter section having selected resistors which can only decrease in value during a failure mode and, in series with the high-pass filter section, a low-pass filter section having selected resistors which can only increase in value during a failure mode, whereby under any failure mode, the pass band of the filter will be reduced; and a level detector having an upper threshold voltage trip point and a lower threshold voltage trip point, both trip points having to be exceeded by the input wave form to produce a proper (square wave) output.