ds18b20 compare temperatures

I am monitoring 4 sensors for my outside wood burner and my geothermal system. What I would like to do is when my outside wood burner input temp (Therm3) drops below 140 F to have an alarm go off. I am very new to coding but was able to make it this far using google and trial and error but I cannot figure out how to compare temperatures.
Any help is appreciated,

Chad

something like this

const int alarmPin = 5;
float alarmLevel = 140;

void setup() 
{
  Serial.begin(115200);
  Serial.println("Start ");

  digitalWrite(alarmPin, LOW);
  pinMode(alarmPin, OUTPUT);
}

void loop() 
{
  float t = getTemperatureF();  // to be written
  
  if (t >= alarmLevel)
  {
    digitalWrite(alarmPin, HIGH);
  }
  else
  {
    digitalWrite(alarmPin, LOW);
  }
}

float getTemperatureF()
{
  return 32;  // to be written, depends on sensor used
}

Thanks, that helped! How can I pull the temperature from sensor 3 only? It appears that I am comparing all the sensors to the alarmlevel value, not just sensor 3.

Thanks for your help,

I do not have a sensor3 , can you send me one?

ok, I got it woot!!

float t = sensors.getTempF(Therm3);

if (alarmlevel > t) // check to see if Therm3 is below alarm level, if so sound alarm.
{
digitalWrite(ledPin, HIGH);
}
else
{
digitalWrite(ledPin, LOW);
}
}

thanks for your help

maybe post the whole code for future reference?