TL;DR. Sit in the drivers seat and spam
The SIFA alarm sounds every so often to make sure the driver is awake.
This doesn't sound by default, you have to flick a switch on a wall if you want it to sound for realism purposes.
For the achievement however, it doesn't have to be on.
All you have to do is spam
you will hear a click. Do this 500 times to unlock the achievement.
You can also, if you prefer, press the pedal manually located under the control center in front of the drivers seat.