user34614: My goal with the code is simple. Let the Piezo buzz when temperature reaches 25 degrees. My piezo is hooked up correctly, because It makes a buzz when the arduino boots or when I put this line of code anywhere else in my code.
I also checked if the If statement was called. And yes it is! So the if statements is happening yet I don't hear a buzz. 
I am aware that I am breaking my seven segmented screen by using the delay. But I don't mind the screen working when the buzzer is. 
void loop()
{
  //local vars
  if (millis() % 5000 <= 10) {
      float lm35TempC = lm35.getTempC();
      sevseg.setNumber(lm35TempC, 2);
      if (lm35TempC > 25.00) {
        tone(1,500,1000);
        delay(3000);  <------- WHERE IT PROBABLY GOES WRONG
      }
      if (lm35TempC < 25.00) {
        noTone(1);
      }
  }
  sevseg.refreshDisplay(); // Must run repeatedly; don't use blocking code (ex: delay()) in the loop() function or this won't work right
}

To conclude: The If-statement is working yet I don't hear a buzz. How does this happen? 
Thanks in Advance!

user37622: You connected the piezo to pin 1? Chose other pin. Pin 1 is Serial TX. You 'pump' PWM to USB.
tone() function will make sound no matter if you have a delay there. You set 1 sec with 1000 as third parameter. It will sound 1 sec and the turn of. You do not need the delay() and noTone().
500 is low frequency. If it sounds only one second, can you catch it?
try tone(TONE_PIN, 4500, 500). with speaker it is a nice beeeep

34614: <p>My goal with the code is simple. Let the Piezo buzz when temperature reaches 25 degrees. My piezo is hooked up correctly, because It makes a buzz when the arduino boots or when I put this line of code anywhere else in my code.</p>

<p>I also checked if the If statement was called. And yes it is! So the if statements is happening yet I don't hear a buzz. </p>

<p>I am aware that I am breaking my seven segmented screen by using the delay. But I don't mind the screen working when the buzzer is. </p>

<pre><code>void loop()
{
  //local vars
  if (millis() % 5000 &lt;= 10) {
      float lm35TempC = lm35.getTempC();
      sevseg.setNumber(lm35TempC, 2);
      if (lm35TempC &gt; 25.00) {
        tone(1,500,1000);
        delay(3000);  &lt;------- WHERE IT PROBABLY GOES WRONG
      }
      if (lm35TempC &lt; 25.00) {
        noTone(1);
      }
  }
  sevseg.refreshDisplay(); // Must run repeatedly; don't use blocking code (ex: delay()) in the loop() function or this won't work right
}
</code></pre>

<p>To conclude: The If-statement is working yet I don't hear a buzz. How does this happen? </p>

<p>Thanks in Advance!</p>
 37622: <p>You connected the piezo to pin 1? Chose other pin. Pin 1 is Serial TX. You 'pump' PWM to USB.</p>

<p>tone() function will make sound no matter if you have a delay there. You set 1 sec with 1000 as third parameter. It will sound 1 sec and the turn of. <strong>You do not need the delay() and noTone()</strong>.</p>

<p>500 is low frequency. If it sounds only one second, can you catch it?</p>

<p>try <code>tone(TONE_PIN, 4500, 500)</code>. with speaker it is a nice beeeep</p>
