The stiffness and topology of ultra-small circular DNAs and DNA/peptide hybrids are exploited to create a transducer of enzyme activity with low error rates. The modularity and flexibility of the concept are illustrated by demonstrating various transducers that respond to either specific restriction endonucleases or to specific proteases. In all cases the output is a DNA oligo signal that, as we show, can readily be converted directly to an optical readout, or can serve as input for further processing, for example, using DNA logic or amplification. By exploiting the DNA hairpin (or stem-loop) structure and the phenomenon of strand displacement, an enzyme signal is converted into a DNA signal, in the manner of a transducer. This is valuable because a DNA signal can be readily amplified, combined, and processed as information.