We use a buzzer that is an important component of our surveillance system. In the event a trespasser bypasses the manual security, our surveillance system will not miss the trespasser. When detected near the restricted area, an alarm is raised with the help of the buzzer, which will alert the security people and force the trespasser to run away.

We make use of a piezo buzzer, which is readily available and cost-effective. A piezo buzzer is built of a piezo-electric material. The working of the piezo buzzer is based on the inverse of the principle of piezo electricity. The principle of piezo electricity states that whenever mechanical pressure is applied on piezo electric material, it generates electricity. And piezo buzzers follow the opposite principle, which states that when a voltage is applied on a piezo electric element, it deforms back and forth (a change in dimension takes place) and produces an audible sound.

Figure 6.13 shows a piezo electric buzzer:

We are using a LED as an indicator. Since we have already discussed LED in detail in Chapter 5, Controlling the Pi, we will not go through it again.