Biased screening at domestic terminal

I WOULD like to air my concern on the biased screening at the Jackson Airport’s domestic terminal.
This incident happened last Wednesday morning at the second screening check.
When the alarm detector beeps, you are forced to remove whatever metal accessories you have or are wearing, even when you are rushing to board a flight.
I was surprised to see a man in police mobile uniform passing through without the mandatory second check even though the alarm went off.
The security guard on duty just smiled at him and allowed him to go to the waiting area.
I would like this parti­cular security company to answer my questions:
l    If the passenger was carrying arms or ammunition, is he allowed to board the plane?
l    What is the point of installing a metal detector?
l    Is there a different law for police officers and ordinary passengers?
l    How can the travelling public be assured security guards are doing their job properly?

Traveller
Port Moresby