8. PIR Motion Alarm

Read the digital output of an HC-SR501 PIR sensor. Publish both the current motion state and a counter when a new motion event begins.

Level: Beginner · Time: 30 minutes

Parts and wiring

ESP32 DevKit V1 and HC-SR501 PIR sensor

PIR	ESP32
VCC	5V / VIN
OUT	GPIO 27
GND	GND

The common HC-SR501 output is typically suitable for ESP32 logic; verify a different module’s output voltage before connecting it.

Complete sketch


#include <PxServ.h>
 
const char* WIFI_SSID = "your_wifi_ssid";
const char* WIFI_PASSWORD = "your_wifi_password";
const char* PXSERV_API_KEY = "your_pxserv_api_key";
const int PIR_PIN = 27;
 
PxServ client(PXSERV_API_KEY);
bool previousMotion = false;
unsigned long eventCount = 0;
 
void setup() {
  Serial.begin(115200);
  pinMode(PIR_PIN, INPUT);
  PxServ::connectWifi(WIFI_SSID, WIFI_PASSWORD);
  Serial.println("Waiting for PIR warm-up...");
  delay(30000);
}
 
void loop() {
  bool motion = digitalRead(PIR_PIN) == HIGH;
 
  if (motion != previousMotion) {
    client.setData("motion/status", motion ? "1" : "0");
    if (motion) {
      eventCount++;
      client.setData("motion/event-count", String(eventCount));
      Serial.println("Motion detected");
    } else {
      Serial.println("Motion ended");
    }
    previousMotion = motion;
  }
  delay(100);
}

Test

Wait for the 30-second warm-up, then move in front of the sensor. The status should become 1 and the event count increase. Reduce sensitivity or move the sensor away from heat and sunlight if it triggers continuously.

Reference: Adafruit PIR guide