Sound Sweep™ and Select a Pest™ Technology (continued): Using the frequency index on the back of The Guardian™ - which shows what animals respond to what sound waves – you can simply adjust the frequency knob to the pest of your choice and say goodbye to that annoying skunk forever. Rather than use a stagnant frequency that may not get the attention of a certain animal, the rise and fall of a fluctuating noise frequency acts like a siren that can’t be ignored. Both repelling methods work on an ultrasonic level, though some frequencies can be slightly audible.