Smart Mailbox Notifier: Get Alerted the Moment Mail Arrives with an ESP8266
Mailboxes tend to sit far from any outlet, and the flap might only open once or twice a day — exactly the kind of problem ESP8266 deep sleep exists for. This project mounts a reed switch on the mailbox flap, keeps the ESP8266 asleep almost all the time, and wakes it only the instant the flap opens to fire off a notification.
How it works
- A small magnet sits on the mailbox flap and a reed switch sits on the box body — when the flap opens, the magnet moves away and the reed switch changes state (open/closed circuit).
- The ESP8266 spends nearly all its time in deep sleep to conserve battery.
- The reed switch’s state change pulls the RST pin low, waking the ESP8266.
- The ESP8266 wakes, connects to WiFi, sends an HTTP POST request to a notification service, then goes right back to deep sleep.
Parts list
- A battery-capable ESP8266 module (e.g. Wemos D1 Mini — ideally a variant with an onboard Li-ion charging circuit)
- Normally-open reed switch + small magnet
- 18650 Li-ion cell, or 2-3 AA cells through a 3.3V boost converter, depending on your power design
- 10kΩ pull-up resistor for the reed switch pin
- A sealed, weatherproof enclosure for the electronics (outdoor mailboxes catch rain splash)
Sample code
#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <WiFiClientSecure.h>
const char* WIFI_SSID = "your-wifi-name";
const char* WIFI_PASS = "your-wifi-password";
const char* NOTIFY_URL = "https://ntfy.sh/my-mailbox"; // or your own webhook endpoint
void sendNotification() {
WiFi.begin(WIFI_SSID, WIFI_PASS);
unsigned long startTime = millis();
while (WiFi.status() != WL_CONNECTED && millis() - startTime < 15000) {
delay(200);
}
if (WiFi.status() == WL_CONNECTED) {
WiFiClientSecure client;
client.setInsecure(); // demo only: skips TLS verification, don't use where security matters
HTTPClient http;
if (http.begin(client, NOTIFY_URL)) {
http.addHeader("Title", "New mail has arrived!");
int responseCode = http.POST("Mailbox flap opened at " + String(millis()));
Serial.printf("Notification sent, response code: %d\n", responseCode);
http.end();
}
} else {
Serial.println("Could not connect to WiFi, skipping this cycle");
}
}
void setup() {
Serial.begin(115200);
delay(100);
Serial.println("Woke from deep sleep - mailbox flap just opened");
sendNotification();
// Go back into indefinite deep sleep until RST is pulled low again
ESP.deepSleep(0);
}
void loop() {
// Never reached - setup() already handled everything and entered deep sleep
}The most important hardware quirk here: on the ESP8266, waking from deep sleep via an external signal requires a jumper wire between GPIO16 and RST. When the reed switch pulls RST low, the board actually resets and re-runs
setup()— this is effectively “wake on reset,” not a conventional GPIO interrupt. If your project needs more flexible wake behavior (multiple pins, RAM state preserved across wake), the ESP32 supportsesp_sleep_enable_ext0_wakeup()/ext1_wakeup()far more cleanly and is worth considering if the RST jumper trick on the ESP8266 feels too fragile.
Common pitfalls
- Long
delay()calls while waiting on WiFi drain the battery fast — if the mailbox location has slow WiFi association, consider caching the IP/channel withWiFi.begin(ssid, pass, channel, bssid, true)to shorten the scan time. - No mechanical debouncing on the reed switch — wind or vibration from passing traffic can jostle the flap and trigger a false wake; mount the magnet and switch firmly and make sure the flap isn’t loose.
- Skipping weatherproofing — an outdoor mailbox takes rain splash and daily humidity swings, so use at least an IP54-rated enclosure and seal cable entry points with silicone.
- Li-ion cells deep-discharged over months of sleep cycles degrade faster — pick a module with a built-in battery protection circuit.
Where to go from here
Add a small weight sensor to tell apart “flap opened to take mail out” from “flap opened because mail arrived,” or add a light sensor to flag when the mailbox is opened at night — a signal worth extra attention.
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