if anything moved in front of the sensor the alarm rings.

Supplies

Microbit board, Buzzer(piezo), PIR sensor and few jumper wires.

Step 1: Connect the Buzzer

now connect the buzzers positive pin to the pin-0 in the microbit.

connect the negative pin of the buzzer to the GND.(ground).

connect the signal pin of the PIR sensor to the Pin-1 in microbit board.

connect the power pin of the PIR sensor to the 3V in microbit.

connect the the Ground pin to the GND pin in microbit.

Now make the code as shown in this picture.

happy microbitting.