General Purpose Analog Amplifier (FX12)The FX12 is an analog amplifier: it will amplify small signals from piezo and other low level sensors for reading by a 0 10V input. Commonly used for knock knock, microphone, and other puzzles where a sequence of analog pulses is detected to trigger an action. This product is just the analog amplifier. You will also need a BAC V with any FX45 expander module (not included). Instead of this product, we typically recommend purchasing our FX12 KNOCK kit