[Konstantinos]

Actually my post was wrong. I was typing fast and as a result, I wrote them opposite.

pawn Код:

public OnPlayerKeyStateChange(playerid, newkeys, oldkeys)
{
    if((newkeys & KEY_CROUCH) && !(oldkeys & KEY_CROUCH))
    {
        // do your code here to open the gate
    }
    return 1;
}

Your method checks for the oldkeys as well as my previous post which was wrong.

Anyways, thanks for replying and I found out my mistake!