Motion alarm with a PIR sensor

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import MotionSensor, LED, Buzzer
from time import sleep

pir = MotionSensor(4)
led = LED(17)
buzzer = Buzzer(18)

print("Sensor warming up...")
sleep(2)
print("Armed. Click the sensor dome to wave a hand.")

while True:
    pir.wait_for_motion()
    print("Motion detected!")
    led.on()
    buzzer.beep(0.1, 0.1, n=5)      # five short beeps
    pir.wait_for_no_motion()
    led.off()
    print("All clear")

How the code works

• A PIR module outputs 3.3 V when it sees movement and 0 V when it does not.
• MotionSensor(4) reads that signal. wait_for_motion() sleeps until it goes high.
• n=5 makes the buzzer stop by itself after five beeps.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.