How to check if the player is in a certain area?

This is pretty simple. You can use Region3.new() . That is one method. You can put a Part in the area that you want the player to be in. Region3

This is the script

local part = -- Put the part path here.
local value = -- Put the value name here(In a string, else it will not work), Has to be in the player and not in one of the children of the player
function CreateRegion3(Part)
    return Region3.new(Part.Position-(Part.Size/2), Part.Position+(Part.Size/2))
end

function FindPlayerInRegion3FromPart(PartToFindPlayerIn)
    local partForRegion = CreateRegion3(PartToFindPlayerIn)
    local playersInRegion3 = workspace:FindPartsInRegion3(partForRegion, nil, math.huge)

    for i, v in pairs(playersInRegion3) do
        local player = game.Players:GetPlayerFromCharacter(v.Parent)
        if player ~= nil then
            if player:FindFirstChild(value) then
                player[value].Value = true
            end
        end
        return player
    end
end

while wait(0.5) do
    FindPlayerInRegion3FromPart(PartToFindPlayerIn)
end

If this does not work, please comment and I will try to fix it. After this you can do the communicating with scripts for the effect.