const int reedPin = 21; // Example GPIO

void setup() {
  pinMode(reedPin, INPUT); // Use internal pull-up
  Serial.begin(115200);
}
void loop() {
  int reedState = digitalRead(reedPin);
  if (reedState == LOW) {
    Serial.println("Magnet detected (Closed)");
  } else {
    Serial.println("No magnet (Open)");
  }
  delay(100);
}