Temperature Alarm

What You'll Build

This is an educational temperature indicator, not a certified alarm or safety device. It watches its surrounding air and sounds when the reading passes your chosen limit. Test it with warm hands or normal room-temperature changes, never against hot liquids, heaters, flames, people, pets, food, or anything where a missed warning could cause harm.

What You Need

• ✓Arduino Uno
• ✓TMP36 analog temperature sensor
• ✓Piezo buzzer
• ✓Red LED
• ✓220Ω resistor

How It Works

A TMP36 sensor outputs a voltage that rises steadily with temperature — 10 millivolts per degree, offset by 500 millivolts at 0 °C. The Arduino reads that voltage on an analog pin, converts it to degrees, and compares it with a limit. If the reading is over the limit, the alarm code runs; otherwise everything stays quiet.

Before You Wire It

Wiring

Step-by-Step Instructions

1. 1

   Wire the sensor the right way round

   TMP36 pinouts can differ from similar-looking sensors, so check the exact part marking and datasheet with an adult. A reversed sensor can get hot quickly. If you smell burning or notice heat, unplug power immediately and let the part cool before touching it.

2. 2

   Convert volts to degrees

   Multiply the reading by 5.0 and divide by 1024 to get volts, then subtract 0.5 and multiply by 100 to get Celsius.

3. 3

   Check against a real thermometer

   Compare your value with a room thermometer. If it is consistently off by a degree or two, add a small correction.

4. 4

   Add the alarm

   Use tone() for the buzzer so you can choose the pitch, and flash the LED in the same rhythm.

5. 5

   Set your limit

   Pick a threshold that makes sense for your test. 30 °C is easy to reach with warm hands.

Arduino Code

const int SENSOR = A0;
const int BUZZER = 8;
const int LED = 7;
const float LIMIT = 30.0;   // degrees C

void setup() {
  pinMode(BUZZER, OUTPUT);
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
}

float readCelsius() {
  float volts = analogRead(SENSOR) * 5.0 / 1024.0;
  return (volts - 0.5) * 100.0;
}

void loop() {
  float t = readCelsius();
  Serial.println(t);

  if (t > LIMIT) {
    tone(BUZZER, 1200);
    digitalWrite(LED, HIGH);
    delay(250);
    noTone(BUZZER);
    digitalWrite(LED, LOW);
    delay(250);
  } else {
    noTone(BUZZER);
    digitalWrite(LED, LOW);
    delay(500);
  }
}

Understanding the Code

Challenges & Upgrades

Troubleshooting

Helpful Resources