Piezo warning buzzer electronic project

A piezo warning buzzer electronic project can that be used for various applications requiring warning system can be built using electronic scheme in the figure below.
The circuit become operational when contact is connected to the power outlet.
When voltage is applied to the circuit determines the start of the oscillator built around the gate N2. This attack one of the entrances of N3. The second input receives a high potential of N3 through resistance R7, which will determine entrance of buzzer in operation.
Meanwhile, at the pin 12 of CD4060 circuit high potential is applied and the circuit is initialized. This integrated circuit is a binary number with 14 stages, built-in oscillator whose frequency is dictated by external components (C2, R3 and R4). After some time (about six seconds), the Q13 output (pin 3) of the integrated circuit goes to of "high" state and N2 oscillator stops by applying a low potential to entry (pin 5) through the gate N1. This command stops buzzer and ensure that it will not ring every time the contact voltage is connected.
If you do not want to use a piezo buzzer can used a speaker version shown in Figure 2 consists of a small speaker ordered a pair of Darlington. Transistors T1 and T2 can be replaced by a single Darlington transistor, ie BC 516.
Circuit can be used in various applications, such as warning to reverse for car.