int Trigpin=12;
int Echopin=11;
int LEDred=8;
int LEDblue=9;
int Buzzerpin=7;

long duration,distance;

void setup(){

  pinMode(Trigpin, OUTPUT);
  pinMode(Echopin, INPUT);
  Serial.begin(9600);
}
void loop(){


digitalWrite(Trigpin, HIGH);
delayMicroseconds(2);
digitalWrite(Trigpin, LOW);
delayMicroseconds(10);

duration=pulseIn(Echopin,HIGH);
distance=duration*0.034/2;

Serial.print("distance:");
Serial.println(distance);

if (distance<400){
digitalWrite(LEDred, HIGH);
tone(Buzzerpin,300,400);
}
else {
  digitalWrite(LEDblue, LOW);
  noTone(Buzzerpin);
}
}