ABSTRACT
A piezo-electric buzzer produces a low-pitched sound suitable for a door alert. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780080959153/a02e7bef-ec09-4853-831d-9795f01199b3/content/fig46_1_OB.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/>
