IoT-Based Smart Women's Safety Device with Heart-Rate Monitoring and Real-Time Alert System

Project Overview

This project is a hybrid online/offline IoT personal safety device designed for women at risk. It integrates biometric monitoring, real-time GPS tracking, GSM emergency SMS alerting, and Firebase cloud telemetry into a single self-contained portable enclosure powered by a LiPo battery with USB-C charging.

The device features a dual-trigger emergency system. The user can manually press a physical panic button for an immediate alert, or the system automatically detects a biometric anomaly when the heart rate falls below 50 BPM or rises above 120 BPM. To prevent false alarms, five consecutive abnormal readings are required before the automatic alert fires. On triggering, the device acquires GPS coordinates, constructs a Google Maps URL, stamps the event with an NTP-sourced Nigeria UTC+1 timestamp, and dispatches an SMS via SIM800L. All events are simultaneously synced to Firebase Realtime Database for remote monitoring.

A 2-second long press on the same panic button resets the system to safe mode, sends a confirmation SMS, and extinguishes the buzzer. The device operates fully offline if Wi-Fi is unavailable: GSM SMS continues to function without any cloud connectivity. A non-blocking millis()-based architecture keeps GPS parsing, heart-rate sampling, button debounce, buzzer control, Firebase sync, and OLED display all running concurrently without any blocking delay() calls in the main loop.

Key Features

• Dual-trigger emergency: short press of panic button fires instant alert; 5 consecutive abnormal BPM readings (BPM < 50 or > 120) trigger automatic alert
• 2-second long press safe-mode reset: cancels active alert, silences buzzer, sends confirmation SMS
• Real-time GPS location: NEO-6M at 115200 baud over UART2; Google Maps URL embedded in every SMS
• NTP-stamped SMS alerts: Nigeria UTC+1 timestamp sourced from pool.ntp.org and formatted DD/MM/YYYY HH:MM:SS
• Firebase Realtime Database: telemetry (BPM, GPS, status) pushed every 6 seconds; emergency contact phone number pulled every 10 seconds
• Remote phone number update: emergency contact changeable via Firebase without reprogramming; OLED popup confirms new contact
• 18-second PPG stabilisation window: filters noise during initial finger placement before active monitoring begins
• Smart 3-beep buzzer pattern: three 200 ms beeps then 3-second silence, cycling indefinitely while alert is active
• SH1106 1.3” OLED live dashboard: shows MODE (SAFE/DANGER), heart-rate state, GPS lock status, and real-time coordinates
• Offline fallback: SIM800L GSM SMS operates without Wi-Fi; Firebase sync silently skipped until reconnected
• Non-blocking firmware architecture: all six concurrent tasks (GPS, button, HR, buzzer, IoT, OLED) driven by millis() timers; zero blocking loops in loop()
• LiPo power system: LX-LCBST USB-C charger module + XL6009 DC-DC step-up boost converter for stable 3.3–5 V rails; slide switch for clean power-on/off

System Architecture

The device is organised into six concurrent subsystems all driven by a single non-blocking loop():

Hardware Components

GPIO Pin Assignments

Heart Rate State Machine

The PPG heart rate subsystem uses a 3-state machine to eliminate the noisy, erratic readings that occur immediately after the user places their finger on the sensor. Only after 18 seconds of confirmed successive beats does the firmware promote to active monitoring mode.

If 7 seconds pass without any beat detection in any non-IDLE state, the machine resets to HR_IDLE. This handles the user removing their finger mid-session without a firmware restart.

// Heart Rate State Machine (inside loop())
if (pulseSensor.sawStartOfBeat()) {
    currentBPM = pulseSensor.getBeatsPerMinute();
    lastBeatTime = currentMillis;

    if (hrState == HR_IDLE) {
        hrState = HR_STABILIZING;
        stabilizeStartTime = currentMillis;
    }
    else if (hrState == HR_STABILIZING) {
        if (currentMillis - stabilizeStartTime > STABILIZE_DURATION) {  // 18 s
            hrState = HR_MONITORING;
            abnormalBeatCount = 0;
        }
    }
    else if (hrState == HR_MONITORING) {
        if (!alertActive) {
            if (currentBPM < 50 || currentBPM > 120) {
                abnormalBeatCount++;
                if (abnormalBeatCount >= 5) {
                    triggerDanger("Auto-Alert: Abnormal Heart Rate (" + String(currentBPM) + " BPM)!");
                    abnormalBeatCount = 0;
                }
            } else {
                abnormalBeatCount = 0;  // normal beat resets counter
            }
        }
    }
}

// Finger-removed timeout: reset to IDLE after 7 s with no beat
if (hrState != HR_IDLE && (currentMillis - lastBeatTime > FINGER_REMOVED_TIMEOUT)) {
    hrState = HR_IDLE;
    currentBPM = 0;
    abnormalBeatCount = 0;
}

Dual-Trigger Alert Logic

Both trigger paths converge on triggerDanger(cause), which sets alertActive = true, fetches the current GPS location and NTP timestamp, builds the SMS body, and dispatches via SIM800L. The 2-second long press calls triggerSafe(), which mirrors the same pattern but clears alertActive and sends a "I am safe now" SMS.

void triggerDanger(String cause) {
    alertActive = true;
    currentTimestamp = getFormattedTime();

    String smsMsg = cause + "\n";
    if (gpsValid) {
        smsMsg += "Please help! Location: " + locationURL + "\n";
    } else {
        smsMsg += "Please help! GPS unavailable.\n";
    }
    smsMsg += "Time: " + currentTimestamp;

    if (WiFi.status() == WL_CONNECTED) {
        Firebase.setString(fbdo, "/Alert_Message",
            cause + " Location: " + locationURL + " | " + currentTimestamp);
    }
    sendSMS(recipientNumber, smsMsg);
}

void triggerSafe() {
    alertActive = false;
    digitalWrite(BUZZER_PIN, LOW);
    currentTimestamp = getFormattedTime();

    String smsMsg = "I am safe now. False alarm or danger passed.\n";
    if (gpsValid) smsMsg += "Current Location: " + locationURL + "\n";
    smsMsg += "Time: " + currentTimestamp;

    if (WiFi.status() == WL_CONNECTED) {
        Firebase.setString(fbdo, "/Alert_Message",
            "Safe Mode Activated. | " + currentTimestamp);
    }
    sendSMS(recipientNumber, smsMsg);
}

OLED Dashboard UI

The SH1106 1.3” OLED runs in U8g2 page-buffer mode (U8G2_SH1106_128X64_NONAME_1_HW_I2C) and refreshes every 1 second. Page-buffer mode renders one horizontal band at a time, requiring less RAM than the full-frame buffer while still producing a flicker-free display. The dashboard has two screen modes:

• Normal dashboard: top-left shows "MODE: SAFE" or "MODE: DANGER!", top-right shows "[WIFI]" or "[X-FI]"; second row shows heart rate state and BPM; rows 3–5 show GPS lock and live latitude/longitude
• New contact overlay: a non-blocking 3-second popup fires whenever Firebase delivers an updated phone number, displaying "NEW CONTACT SYNCED" with the local (0-prefix) formatted number and "System Updated." text, then reverts to the normal dashboard automatically

The OLED also shows dedicated boot and SMS-sending screens: on startup it displays the project title and student matriculation number for 3 seconds; while an SMS is being dispatched it shows "SENDING SMS... Please Wait." to inform the user.

void updateOLED() {
    display.firstPage();
    do {
        display.setFont(u8g2_font_6x10_tf);

        // New contact overlay: 3-second non-blocking popup
        if (showNewContactOverlay && (millis() - newContactOverlayTime < 3000)) {
            display.drawStr(10, 15, "NEW CONTACT SYNCED");
            display.drawHLine(0, 22, 128);
            display.drawStr(10, 40, displayContactNumber.c_str());
            display.drawStr(10, 55, "System Updated.");
        }
        else {
            showNewContactOverlay = false;

            // Wi-Fi status (top-right)
            display.drawStr(92, 10, (WiFi.status() == WL_CONNECTED) ? "[WIFI]" : "[X-FI]");

            // Alert mode (top-left)
            display.drawStr(0, 10, alertActive ? "MODE: DANGER!" : "MODE: SAFE");

            // Heart rate row
            String hrStr = "HR: ";
            if      (hrState == HR_IDLE)        hrStr += "-- (Place Finger)";
            else if (hrState == HR_STABILIZING) hrStr += String(currentBPM) + " (Reading...)";
            else                                hrStr += String(currentBPM) + " BPM (Active)";
            display.drawStr(0, 24, hrStr.c_str());

            // GPS rows
            if (gpsValid) {
                display.drawStr(0, 38, "GPS: LOCKED");
                display.drawStr(0, 50, ("Lat: " + String(latitude, 5)).c_str());
                display.drawStr(0, 62, ("Lng: " + String(longitude, 5)).c_str());
            } else {
                display.drawStr(0, 38, "GPS: SEARCHING...");
                display.drawStr(0, 50, "Lat: --");
                display.drawStr(0, 62, "Lng: --");
            }
        }
    } while (display.nextPage());
}

Firebase & IoT Connectivity

The device connects to Firebase Realtime Database using the FirebaseESP32 library with a legacy token. Three Firebase paths are used:

• /Telemetry: a JSON object pushed every 6 seconds containing BPM, Status ("SAFE" or "DANGER"), Latitude, Longitude, and LocationURL
• /Phone_Number: a string read every 10 seconds; if a new number is detected it replaces recipientNumber in RAM and triggers the OLED popup overlay
• /Alert_Message: a string written immediately on each danger or safe event with the cause, location URL, and NTP timestamp

The NTP client syncs to pool.ntp.org with a UTC+1 offset (3600 seconds) for Nigeria local time. Timestamps are formatted as DD/MM/YYYY HH:MM:SS using localtime() and snprintf().

void sendDataToFirebase() {
    FirebaseJson telemetryData;
    if (gpsValid) {
        telemetryData.set("Latitude",    latitude);
        telemetryData.set("Longitude",   longitude);
        telemetryData.set("LocationURL", locationURL);
    } else {
        telemetryData.set("LocationURL", "Unavailable");
    }
    telemetryData.set("BPM",    currentBPM);
    telemetryData.set("Status", alertActive ? "DANGER" : "SAFE");
    Firebase.set(fbdo, F("/Telemetry"), telemetryData);
}

void readPhoneNumberFromFirebase() {
    if (Firebase.getString(fbdo, "/Phone_Number")) {
        String fetched = fbdo.stringData();
        if (fetched.length() > 5 && recipientNumber != fetched) {
            recipientNumber = fetched;
            // Convert +234 / 234 prefix to local 0-prefix for OLED display
            displayContactNumber = fetched;
            if (displayContactNumber.startsWith("+234"))
                displayContactNumber = "0" + displayContactNumber.substring(4);
            else if (displayContactNumber.startsWith("234"))
                displayContactNumber = "0" + displayContactNumber.substring(3);
            showNewContactOverlay = true;
            newContactOverlayTime = millis();
        }
    }
}

String getFormattedTime() {
    timeClient.update();
    time_t rawTime = timeClient.getEpochTime();
    struct tm *ti = localtime(&rawTime);
    char buffer[25];
    snprintf(buffer, sizeof(buffer), "%02d/%02d/%04d %02d:%02d:%02d",
             ti->tm_mday, ti->tm_mon + 1, ti->tm_year + 1900,
             ti->tm_hour, ti->tm_min, ti->tm_sec);
    return String(buffer);
}

Circuit Diagrams

The circuit was designed in Proteus and exported as both a colour schematic and a black-and-white reference diagram. The final PCB was hand-soldered on a 9×15 cm copper perfboard with female header rows for all removable modules.

Colour circuit schematic (Proteus)

Black & white reference schematic (Proteus)

Firmware: Key Code Excerpts

The complete sketch is ~600 lines of Arduino/C++. Below are the three most architecturally significant excerpts. All six subsystems in loop() use millis()-based timers so none block the others.

Button Debounce & Press-Duration Logic

// 50 ms debounce + duration measurement for dual-trigger button
int rawButtonState = digitalRead(BUTTON_PIN);
if (rawButtonState != lastRawButtonState) lastDebounceTime = currentMillis;

if ((currentMillis - lastDebounceTime) > DEBOUNCE_DELAY) {  // 50 ms
    if (rawButtonState != stableButtonState) {
        stableButtonState = rawButtonState;
        if (stableButtonState == LOW) {   // pressed
            buttonPressStart = currentMillis;
            buttonPressed = true;
        } else {                          // released
            buttonPressed = false;
            unsigned long pressDuration = currentMillis - buttonPressStart;
            if (pressDuration >= LONG_PRESS_TIME) {   // >= 2000 ms
                triggerSafe();
            } else if (pressDuration > 50) {          // short press
                if (!alertActive) triggerDanger("Manual Panic Button Pressed!");
            }
        }
    }
}
lastRawButtonState = rawButtonState;

Non-Blocking 3-Beep Buzzer Pattern

// Three 200 ms beeps then 3 s silence, cycling while alertActive
if (alertActive) {
    if (!inSilencePeriod) {
        if (currentMillis - lastBuzzerTime >= 200) {
            buzzerState = !buzzerState;
            digitalWrite(BUZZER_PIN, buzzerState ? HIGH : LOW);
            lastBuzzerTime = currentMillis;
            if (!buzzerState) {         // falling edge = one beep completed
                beepCount++;
                if (beepCount >= 3) {   // three beeps done
                    inSilencePeriod = true;
                    beepCount = 0;
                }
            }
        }
    } else {
        if (currentMillis - lastBuzzerTime >= 3000) {
            inSilencePeriod = false;
            lastBuzzerTime = currentMillis;
        }
    }
}

SMS Dispatch via SIM800L AT Commands

void sendSMS(String phoneNumber, String message) {
    // Show "SENDING SMS..." on OLED during the blocking AT sequence
    display.firstPage();
    do {
        display.setFont(u8g2_font_6x10_tf);
        display.drawStr(10, 30, "SENDING SMS...");
        display.drawStr(10, 45, "Please Wait.");
    } while (display.nextPage());

    GSM_SERIAL.println("AT");               delay(500);
    GSM_SERIAL.println("AT+CMGF=1");        delay(500);   // text mode
    GSM_SERIAL.println("AT+CMGS=\"" + phoneNumber + "\""); delay(500);
    GSM_SERIAL.print(message);              delay(500);
    GSM_SERIAL.write(26);   // Ctrl+Z = send
    delay(2000);
}

void setup() {
    Serial.begin(115200);
    pinMode(BUTTON_PIN, INPUT_PULLUP);
    pinMode(BUZZER_PIN, OUTPUT);
    pinMode(WIFI_LED_PIN, OUTPUT);
    pinMode(GPS_LED_PIN, OUTPUT);
    digitalWrite(BUZZER_PIN, LOW);
    digitalWrite(WIFI_LED_PIN, LOW);
    digitalWrite(GPS_LED_PIN, LOW);

    Wire.begin();
    display.begin();
    showBootScreen();   // 3-second splash: project title + student ID

    GPS_SERIAL.begin(115200, SERIAL_8N1, GPS_RX_PIN, GPS_TX_PIN);  // UART2

    GSM_SERIAL.begin(115200, SERIAL_8N1, GSM_RX_PIN, GSM_TX_PIN);  // UART1
    delay(3000);
    GSM_SERIAL.println("AT+CMGF=1");  // set text mode

    analogReadResolution(10);
    pulseSensor.analogInput(PULSE_INPUT);     // GPIO 36
    pulseSensor.blinkOnPulse(PULSE_BLINK);    // GPIO 2
    pulseSensor.setThreshold(THRESHOLD);      // 550
    pulseSensor.begin();

    connectToWiFi();
    timeClient.begin();
    timeClient.update();
    setupFirebase();
}

void showBootScreen() {
    display.firstPage();
    do {
        display.setFont(u8g2_font_6x10_tf);
        display.drawStr(10, 12, "SMART SAFETY");
        display.drawStr(25, 24, "DEVICE");
        display.drawHLine(0, 30, 128);
        display.drawStr(0, 42, "UGWOKE CHIZARAM P.");
        display.drawStr(0, 54, "21CK029347");
    } while (display.nextPage());
    delay(3000);
}

Project Photos

75 photos documenting the project from individual components through PCB assembly, enclosure integration, and final live demonstration.

Components, January 2026

SIM800L EVB GSM module with whip antenna and u.FL pigtail

LiPo battery (angle 1)

LiPo battery (angle 2)

LiPo battery (wider shot)

Black heat shrink tubing loop

Panel-mount DC charging jack

Female single-row pin header strips

9 cm × 15 cm copper perfboard

ESP32 dev board on anti-static foam (front)

ESP32 dev board (side view)

Active buzzer with BC547 NPN transistor driver

Buzzer driver circuit (angle 2)

Status LEDs: green (Wi-Fi), yellow (GPS)

Blue metal-film resistors

Blue tactile panic button with cap (angle 1)

Panic button (angle 2)

LX-LCBST USB-C LiPo charger module (front)

LX-LCBST charger module (back)

NEO-6M GPS module (GY-GPS6MV2) with ceramic patch antenna

NEO-6M GPS + patch antenna (angle 2)

SH1106 1.3” OLED in protective plastic case

SH1106 OLED display module

Purple LiPo power board with USB-A output (front)

LiPo power board USB-C input side

3-pin slide power switch (angle 1)

Slide switch (angle 2)

Slide switch (side view)

KAINA CF-10 0.8 mm 63/37 solder wire

Solder wire spool (rotated)

XL6009 DC-DC step-up boost converter (front)

XL6009 converter (back ("DC-DC STEP-UP" label))

Multi-colour Dupont jumper wire ribbon

Grey flat ribbon cable (FFC)

DFRobot PPG Sensor & GPS Wiring, February 2026

DFRobot Gravity Analog Heart Rate Sensor SEN0203 (back/SMD view)

NEO-6M GPS with ribbon cable (angle 2)

PCB Assembly, February 2026

Perfboard with female headers being soldered (copper side)

Perfboard headers (angle 2)

More headers soldered; GPS antenna and module in background

ESP32 on perfboard with NEO-6M GPS connected via ribbon cable

Developer's hand holding SIM800L; ESP32+perfboard below on workbench

SIM800L showing SIM CARD slot

SIM800L close-up with pull-up resistors connected to ribbon cable

SIM800L + NEO-6M GPS connected via ribbon cables

ESP32 on perfboard with SIM800L and GPS integrated

Active buzzer with resistor and heat-shrink on wire

Buzzer top view showing blue resistor

First full assembly: ESP32, SIM800L, GPS, buzzer all connected

Handwritten GPIO pin assignments: GSM TX-25/RX-33, GPS TX-17/RX-16, Pulse-36, LEDs-19/4

Advanced assembly with OLED, GPS, SIM800L, panic button, and LEDs integrated

Battery & Enclosure Integration, February 2026

Complete system on workbench: all modules including LiPo and DFRobot sensor

Complete system workbench layout (angle 2)

System in black electronic project box enclosure with all modules connected

Device being installed in black electronic project enclosure

Final Device & Live Demonstration, May 2026

Developer with completed device and DFRobot sensor box

Developer with completed device (angle 2)

Developer holding completed device (above) and DFRobot sensor box (below)

Developer with device and DFRobot sensor box

Developer displaying completed device and PPG sensor

Developer holding labeled device prominently

Developer holding DFRobot PPG finger-clip sensor and completed device

Device showing BPM SENSOR port label side

Developer with PPG finger-clip and completed device

Completed device: OLED, GPS antenna, status LEDs, GSM whip antenna, DFRobot PPG connected

Completed device (angle 2)

Completed device (rotated view)

DFRobot SEN0203 box alongside completed device with GSM antenna

"Gravity Heart Rate Sensor" label clearly visible on DFRobot box

Device showing "BPM SENSOR" port label with DFRobot sensor box

Device rear showing "BUZZER" label

Device showing "PROGRAMMING PORT" and "PANIC BUTTON" (yellow button) labels

Device showing "CHARGING STATUS", "CHARGING PORT", and "HEART RATE SENSOR" connector

Device powered on: OLED shows MODE: SAFE, live GPS coordinates; DFRobot green LED lit

End-to-end proof: OLED showing live GPS + smartphone displaying received SMS with Google Maps location pin

Live demo: SMS alert received with Google Maps location (angle 2)

Complete device overhead flat-lay: enclosure with OLED, GPS antenna, PPG clip sensor, power switch, and charging port labels

Project Links

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Best regards,
Damilare Lekan, Adekeye.