The first read

/*
  Door Sensor - first read                              TK107 / /p/tk107

  Wiring. Count from the square pad on the TinkerBlock board, parts
  up, header at the bottom:

    GND    -> GND
    3V3    -> 3V3 on an ESP32, ESP32-S3 or Pico; 5V on an Uno.
              Your board's logic voltage: this pin powers nothing,
              it is the level a closed sensor puts on SIGNAL.
    NC     -> nothing   (unconnected on the board)
    SIGNAL -> GPIO 4 on an ESP32-S3, GPIO 25 on an ESP32,
              D2 on an Uno, GP15 on a Raspberry Pi Pico

  The sensor: its two wires go under the two screws of the terminal
  block. Either way round; the sensor is a plain switch.

  Arduino IDE
    Tools > Board                 your board, e.g. ESP32S3 Dev Module
    Tools > Port                  the one that appears when you plug in
    Tools > USB CDC On Boot       Enabled   (ESP32-S3 only)
    No library needed.
*/

// The pin SIGNAL is wired to.
// Uno: 2. ESP32: 25. ESP32-S3: 4. Pico: 15.
const int DOOR_PIN = 4;

int last = -1;   // nothing read yet

void setup() {
  Serial.begin(115200);

  // The board has no pull-down and no pull-up. While the sensor is
  // open, SIGNAL is connected to nothing and floats; a closed sensor
  // puts VCC on it. So the pin must pull itself LOW: INPUT_PULLDOWN.
  // INPUT_PULLUP would be wrong: open would read HIGH, closed would
  // read HIGH, and the two could never be told apart.
#ifdef INPUT_PULLDOWN
  pinMode(DOOR_PIN, INPUT_PULLDOWN);
#else
  // An Uno or Nano has no internal pull-down. Fit a 10 kOhm resistor
  // from SIGNAL to GND, or this pin will read noise while open.
  pinMode(DOOR_PIN, INPUT);
#endif
}

void loop() {
  int level = digitalRead(DOOR_PIN);

  // The first pass always prints: that is the state at power-up.
  if (level != last) {
    if (level == HIGH) {
      Serial.println("door closed (magnet near)");
    } else {
      Serial.println("door open");
    }
    last = level;
  }

  delay(10);
}

"""
  Door Sensor - first read, MicroPython                 TK107 / /p/tk107

  Wiring. Count from the square pad on the TinkerBlock board, parts
  up, header at the bottom:

    GND    -> GND
    3V3    -> 3V3   (your board's logic voltage: this pin powers
                     nothing, it is the level a closed sensor puts
                     on SIGNAL)
    NC     -> nothing   (unconnected on the board)
    SIGNAL -> GPIO 4 on an ESP32-S3, GPIO 25 on an ESP32,
              GP15 on a Raspberry Pi Pico

  The sensor: its two wires go under the two screws of the terminal
  block. Either way round; the sensor is a plain switch.

  Thonny
    Run > Configure interpreter   MicroPython (ESP32) or
                                  MicroPython (Raspberry Pi Pico)
    Save it to the board as main.py to run it on every power-up.
    Nothing to install: machine and time are built in.
"""

from machine import Pin
import time

# The GPIO SIGNAL is wired to.
# ESP32: 25. ESP32-S3: 4. Pico: 15.
DOOR_PIN = 4

# The board has no pull-down and no pull-up. While the sensor is
# open, SIGNAL is connected to nothing and floats; a closed sensor
# puts VCC on it. So the pin must pull itself LOW: Pin.PULL_DOWN.
# Pin.PULL_UP would be wrong: open would read 1, closed would read
# 1, and the two could never be told apart.
door = Pin(DOOR_PIN, Pin.IN, Pin.PULL_DOWN)

last = None    # nothing read yet, so the first pass always prints
while True:
    level = door.value()
    if level != last:
        if level:
            print("door closed (magnet near)")
        else:
            print("door open")
        last = level
    time.sleep_ms(10)