Hi, what is the cabin Alt warning Alarm in Fokker 100.?

Helicopters don't generally fly high enough for cabin pressurization to be necessary.

Before going into the description of "Sharp Pain" it must be clear that a flight consists of three major phases i.e, takeoff/climb, cruise and descent/landing. All the three phases require differernt PRESSURIZATION SEQUENCES to be maintained inside the cabin to maintain the atmospheric pressure conditions that are almost indentical to that of the sea level, normally 14.7 Psi (however the pressure inside the cabin is slightly lower thatn this value). This "Sharp Pain" in the forehead is associated with these pressurization sequences. The pressurization sequence starts as soon as the aircraft starts running on the runway and the cabin pressure is actually increased (as if the aircraft is diving down below the sea level !!!!). This increase in cabin pressure is necessary to counter the effect of reduced atmospheric pressure at higher altitudes. As a result of this PRE-PRESSURIZATION, a sort of pain is felt in the forehead while the aircraft is still on the ground during takeoff phase !!!! Similar sort of experince is witnessed during the descent phase when the ears start aching because of the increase in cabin pressure as the altitude decreases.

In this answer I have assumed that the reader is aware of the concept of CABIN PRESSURIZATION of an aircraft. If this concept isn't clear I would be more than happy to explain it in order to better understand why PRESSURIZATION is necessary which ultimately has to do a lot with the Sharp Pain phenomenon !!!!!!

what are the sources of pressurization and its components

While the pressure outside the aircraft is very low, cabin pressurization allows pilots to pressurize the aircraft cabin to about 11.5 psi. They try to keep the cabin pressurized to make it seem like the air at around 7,000 feet. That's why your ears pop.