This is a small sample of how you could use it.

And this is the code done in the arduino ide :

#define echo 8
#define trig 7
long duration,distance;

void setup() {
  
  Serial.begin(9600);
  pinMode(echo,INPUT);
  pinMode(trig,OUTPUT);
  pinMode(5,OUTPUT);
}

void loop() {
  
digitalWrite(trig,LOW);
delayMicroseconds(2);
digitalWrite(trig,HIGH);
delayMicroseconds(10);
digitalWrite(trig,LOW);

duration=pulseIn(echo,HIGH);
distance=(duration/(2*29));

if(distance>=500 || distance<=0){
  Serial.println("____");
  }
else{
  Serial.print(distance);
  Serial.println("cm.");
  digitalWrite(5,LOW);
}
if(distance<=45 && distance>=1){// distance in which the bracelet vibrates, you can edit according to your need

  digitalWrite(5,HIGH);
  Serial.println("Alarm!!!");
}
delay(400);
}