Is my application SECURED.. How to protect ?

If you are simply validate the serial number from the DB to the input, it is not secure. The if(input serial== db serial ) is just a simple jump instruction in the disassembly. Change the jump other way is just change a byte value in a hash editor.

What you can do is have the serial digested with a salt and keep the serial and the resulted hash af ter digestion has to be custom encrypted and stored in the global memory. You decryption function should be strong enough, not possible to reverse engineering. Check the validity of this salt digested hash against the serial in many places of your application. So it is not simple a jump, but the hacker not escaped from providing a valuable serial or complete reverse engineering your app.

Apart from that keep the serial in the database encrypted

hope this helps.

I am adding more points here as per your question.

a light weight comparing function based on two global variable will not be a significant issue in performance, so can be called in many places.

Keeping fake function names only help to prevent newbie hackers.

The detailed work flow of what I suggested here is...

1) When use swipe, digest the input serial in a way and store in the app memory. Not the same way encrypted as you did for the original serial. Because if you did the same way this input supposed to result in the same hash you stored in the database. As you are going to get the real hash also in the app, a hacker can swap the real hash to the input hash. Then comparison of both result fruitful. So this input has to hash in a different way than you did for the original hash and it result in a different hash.
2) Get the encrypted serial from the database and store in memory.

3) Now the input hash you stored in step 1 and real hash from database in step 2 has to be subjected to mathematical operations. For example if the user input/ swipe in correctly the mathematical operations may result in zero. Divide a zero with other number will result in a exception. So if incorrect serial is provided it will be result in exception. On the exiting event you can show the message of unauth user.

The basic idea is not using an if condition, but a complex mathematical operation which results in an exception if not provided correct serial.

Checking this function in different major functions of your app doesn't significantly affect the performance as it is simply a few math operations on a two variables in memory which cost a few CPU cycles, not big issue in present day computers. However the little performance issue (though insignificant) will be a tradeoff when security given importance