Bluetooth and accelerometer information seding

im new to this site and programming so im sorry if i put my question at the wrong place or if im hard to understand.

im trying to make a device with a accelerometer that will read a cars acceleration.

when the car is making an unusual acceleration i want this to trigger a call in the app. do i set the values/span for the unusual accelerations in the app code or in my arduino code? the app will be made in app inventro i think but not quite sure. if its in the app i think i can figure it out but if it in the arduino code i dont really understand how i will send all accelerations and also point out the unusual ones?

As well as having a variable for the acceleration, have a second variable (boolean) for unusual acceleration. Send both to your app.

what microcontroller are you using?
do you intend to use Bluetooth Classic or BLE to communicate with the smartphone app?

Can be done on either end.
My rule of thumb is to do most data processing on the most powerful device. That means it would happen in the app if I were doing it.