Detecting if a Monster has "Vision" of a player?

I've actually made a script that does this, you can use it if you want.

local fov = 90 -- This is the monsters field of view
local dist = 50 -- This is the monsters view distance
local monster = script.Parent.Parent.Character.Head -- Change this to the monsters position

function MakeRay(startPos, endPos, show) -- Creates a new ray
		local ray = Ray.new(startPos, endPos)
		local obj, endPoint = Workspace:FindPartOnRay(ray)
		if show then -- This is for debugging. It will make the rays visible
			local rayPart = Instance.new("Part", Workspace)
			rayPart.Name          = "RayPart"
        	rayPart.BrickColor    = BrickColor.new("Bright red")
        	rayPart.Transparency  = 0.5
        	rayPart.Anchored      = true
        	rayPart.CanCollide    = false
        	rayPart.TopSurface    = Enum.SurfaceType.Smooth
        	rayPart.BottomSurface = Enum.SurfaceType.Smooth
        	rayPart.formFactor    = Enum.FormFactor.Custom
        	rayPart.Size          = Vector3.new(0.2, 0.2, dist)
        	rayPart.CFrame        = CFrame.new(startPos, Vector3.new(endPos.x,1.5,endPos.z)) * CFrame.new(0, 0, -dist/2)
			game.Debris:AddItem(rayPart, 0.1) -- Add the part to Debris so it will remove itself after 0.1 second
		end
		return obj -- Return any found objects with ray
end

while true do
	local start = -180-(fov/2) -- Give the ray the right lookVector
	for t = start, start+fov, 5 do -- You can change the 5 to another number as long as it's dividable by the fov. This represents the distance between each endPoint of the ray.
		local target = monster.CFrame -- Set the target to yourself
					* CFrame.new(dist*math.sin(math.rad(t)), monster.Position.Y, dist*math.cos(math.rad(t))) -- Add the radians
					* monster.CFrame.lookVector	-- Get the lookVector of the monster
		local hit = MakeRay(monster.CFrame.p, target, true) -- Create a new ray. Set the last value to false if you're done debugging.
		if hit then -- If the ray has a hit
			if hit.Parent:FindFirstChild("Humanoid") then -- If the hit is a humanoid
				print("Humanoid in sight")
			end
		end

	end
	game:GetService("RunService").RenderStepped:wait()
end