[VonLeeuwen]

Code:

stock IsPlayerInArea(playerid, Float:max_x, Float:min_x, Float:max_y, Float:min_y)
{
new Float:X, Float:Y, Float:Z;
GetPlayerPos(playerid, X, Y, Z);
if(X <= max_x && X >= min_x && Y <= max_y && Y >= min_y) return 1;
return 0;
}

Add that someone in the script (not in callback),

Then,

pawn Code:

forward InArea(playerid); // on top

SetTimer("AreaCheck", 1000, true); // at 'onplayerspawn'

public InArea
{
if(IsPlayerInArea(playerid, max_X, min_X, max_Y, min_Y) // add your own min_X, max_x, min_Y, and max_Y
{
 SendClientMessage(playerid,0xFF0000AA,"You are now in range.");
}
return 1;
}