Abstract: An electronic animal repellant apparatus includes a microphone for detecting environmental sound, a detection circuit for detecting the presence of a particular species of animal in the vicinity of the repellant apparatus, a timing and activation circuit, and a plurality of animal repellant or frightening devices. The microphone produces an input signal fed to the detection circuit that has a frequency content representative of the frequency spectrum of the environmental sound. The input signal is compared to a pre-determined frequency envelope characteristic of the sound spectrum of the particular animal species and a trigger signal is produced when the presence of the particular animal is detected. The detection circuit includes a band-pass filter and a negative feedback band-reject filter, each having readily removable and replaceable components for changing the pre-determined frequency envelope for different species of animal to be repelled.