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Hello everyone, I have a 12v siren with two inputs(red,black), a 12v shock sensor with 3 wires(blue,red,black) and a 12v JD1915 4pins relay..How can I connect the entire circuit to make up an alarm system when the shock sensor receives a shock? Thanks in advance for your precious time

I am afraid that will HIGHLY depends on your "shock sensor".

I am aware of tilt sensor, basically a kind of switch (liquid mercury or rolling ball) which acts as a ... switch. Only two wires, one in and one out.

And of accelerometer like the ADXL335, 5 pins ( Voltage, Ground, X, Y and Z ) which returns an analog voltage, at the X, Y and Z pins, dependant of the acceleration in the direction (each direction assumed orthogonal to each other).

In this case, it could be as simple as to use the desired pin connected to the gate of an NMOS transistor used as a switch, such that when the voltage becomes high enough, the transistor starts to conduct. Since the signal could be short, you may have to keep its "memory", to remember that it happened. If you need extra sophisitcation, plug the ADLX335 to a ADC pin of an Arduino, as example, and determine your "rules" by software (which is easier to modifiy, imho, than to mofified a PCB), given the registred voltages at the X, Y and Z pins (or just one of them, if it is enough).

There are more sophiticated accelerometers available too, if the implied shock detection requires it. But I am not aware of any with just three wires ( three pins). You can give more details about the one you intend to use?