Guard the fridge

Why it’s here

Open the door and wait for the alarm; close it to reset the timer.

How it works

A magnetic reed switch tells you when a door has been open too long. A persistent open state must exceed the delay. Closing the door resets the elapsed time. This guided model targets the original ESP32 and Arduino-ESP32 3.x; radio, acoustics, loads and mechanics are simplified.

Try it

1. Open this experiment
2. Open the door and wait for the alarm; close it to reset the timer.

Connections

• GPIO 27 / GND — Reed switch · INPUT_PULLUP
• GPIO 25 — Passive buzzer signal

Example sketch

unsigned long openedAt = 0;
// Reed switch between GPIO 27 and GND; magnet closes it.

void setup() {
  pinMode(27, INPUT_PULLUP);
  ledcAttach(25, 2000, 8);
}

void loop() {
  bool open = digitalRead(27) == HIGH;
  if (!open) openedAt = millis();
  ledcWriteTone(25, open && millis() - openedAt >= 3000 ? 880 : 0);
}

Check your understanding

Why does the alarm wait?