The device is a simple comparator circuit driven by an infrared receiver (IR) IC. The positive pin of the infrared receiver IC is connected to Rs1/Rs2 resistors connection node. When the infrared receiver IC receives the signal the IR IC output voltage falls from 5 V to 0 V. This causes the voltage at the positive comparator pin to fall below the negative comparator pin. The comparator then provides the current to the buzzer. I included the 470 uF capacitor to filter any power supply surges from the buzzer. The Rs2 resistor is needed to saturate the zener diode and thus ensure that the voltage across the IR receiver IC does not increase to a value much more than 5 V. I used wire wrap to connect my circuit. I did not use a soldering iron. This device is sold as a kit on https://tindie.com