> problem
I needed a simple motion detection system for my garage. When someone enters, it should trigger a local buzzer and send a notification to my phone — all running locally, no cloud required.
> hardware
- ESP32 Dev Board × 1
- HC-SR501 PIR Sensor × 1
- Active Piezo Buzzer × 1
- Status LED × 1
- Breadboard + Wires × 1
> wiring architecture
graph LR
A[PIR Sensor] -->|GPIO 27| B[ESP32]
B -->|GPIO 26| C[Piezo Buzzer]
B -->|GPIO 25| D[Status LED]
B -->|WiFi| E[Telegram API]
> logic flow
sequenceDiagram
participant P as PIR Sensor
participant E as ESP32
participant B as Buzzer/LED
participant T as Telegram
P->>E: Motion Detected (High Signal)
E->>B: Trigger Alarm (PWM)
E->>T: Send Secure Alert
T->>E: Acknowledge
Note over E,B: Alarm active for 30s
E->>B: Reset System
> code
void setup() {
pinMode(PIR_PIN, INPUT);
pinMode(BUZZER_PIN, OUTPUT);
attachInterrupt(digitalPinToInterrupt(PIR_PIN), onMotion, RISING);
}> result
The HC-SR501 is surprisingly sensitive. I had to turn down its sensitivity potentiometer slightly to avoid false triggers from small vibrations. The interrupt-driven approach means no motion events are missed.
> SECURITY_LOG.SH
[2026-05-18 22:15:10] INFO: System armed. Monitoring GPIO 27...
[2026-05-18 23:42:01] ALERT: MOTION DETECTED - SECTOR 1 (GARAGE)
[2026-05-18 23:42:02] SUCCESS: Telegram notification sent to OPERATOR_01
[2026-05-18 23:42:32] INFO: Alarm timeout. Re-arming system...
[2026-05-18 23:42:33] SUCCESS: System ready.