#define trigger 9
#define echo 10
#define bell 7
long timeNeeded;
float distance;
void setup() {
  Serial.begin(9600); 
  pinMode(trigger,OUTPUT); 
  pinMode(echo,INPUT); 
  pinMode(bell, OUTPUT); }
void loop() {
digitalWrite(trigger,LOW); 
delayMicroseconds(2);
digitalWrite(trigger, HIGH);
delayMicroseconds(10);
digitalWrite(trigger, LOW);
timeNeeded = pulseIn(echo, HIGH);
distance= timeNeeded * 0.034/2;
Serial.print("Distance: ");
Serial.println(distance);
if(distance<1000){
  for(int i=0; i<20;i++){
  digitalWrite(bell, HIGH);
  delay(100); 
  digitalWrite(bell,LOW);}}
delay(100);
}