Knock sensor module and a digital 13   interface, built-in LED build a simple circuit to produce percussion   flasher. Interface comes with digital LED, will knock sensor connected   digital 3 interface, when percussion sensor senses measure to percussive   signals, LED flashing light.
       
Routines source code:
int Led = 13;// define LED Interface
int Shock = 3;// define the percussion Sensor Interface
int val;// define numeric variables val
void setup ()
{
pinMode (Led, OUTPUT) ;// define LED as output interface
pinMode (Shock, INPUT) ;// define knock sensor output interface
}
void loop ()
{
val = digitalRead (Shock) ;// read digital interface is assigned a value of 3 val
if (val == HIGH) // When the percussion when the sensor detects a signal, LED flashes
{
digitalWrite(Led, LOW);
}
else
{
digitalWrite(Led, HIGH);
}
}