Door reed sensor on Raspberry Pi with phone notifications

Also available in French.

Know when the front door, shed or cupboard opens: a two-wire reed switch needs no sensor battery— the Pi detects open/close. This script sends ntfy push (free, open source) and optionally publishes a door entity in Home Assistant via MQTT.

Goal

Detect open and close.
Push on open (or only when open too long—see below).
Optional MQTT binary sensor in HA.

Time, level, parts

Time	Level	Budget
~45 min	Beginner	Reed switch is inexpensive—check retailers

Reed (normally open, closes with magnet): UK · US

Wiring

Internal pull-up—no external resistor.

Reed	Pi (physical)
Wire 1	11 (GPIO17)
Wire 2	9 (GND)

Door closed = magnet near = contact closed = GPIO low. Never apply external voltage to the reed line.

Pi prep

Same venv pattern as our other Pi sensor guides (Bookworm, gpiozero + lgpio):

sudo apt update
sudo apt install -y python3-venv python3-gpiozero python3-lgpio
mkdir -p ~/capteurs && cd ~/capteurs
python3 -m venv --system-site-packages venv
source venv/bin/activate
pip install paho-mqtt   # if using HA

ntfy: install the app, subscribe to a long random topic on ntfy.sh (public topics are readable if guessed) or self-host. Set NTFY_URL=https://ntfy.sh/your-secret-topic.

Script: porte_reed_notification.py.

Home Assistant (optional)

Mosquitto + MQTT integration; dedicated user; discovery creates binary_sensor door entity.

Smarter alert: open too long

Instead of every open, notify only if open 5 minutes:

alias: Front door left open
triggers:
  - trigger: state
    entity_id: binary_sensor.raspberry_pi_door_front_door
    to: "on"
    for: "00:05:00"
actions:
  - action: notify.notify
    data:
      message: "Front door open for 5 minutes."

Run the script without NTFY_URL if you only want this HA automation.

systemd

porte-reed.service with Environment=NTFY_URL=... and MQTT_HOST=... — enable on boot.

Troubleshooting

Inverted logic: swap when_pressed / when_released for normally-closed reeds.
Double alerts: increase bounce_time to 0.2–0.3 s.
No push: curl -d test https://ntfy.sh/your-topic from the Pi.

Sources: gpiozero Button · ntfy publish · HA MQTT binary sensor.

Also: garage door ESP32 · PIR motion.

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