How to detect if a Model is overlapped with another object?

Very accurately? You'll have to check every part in the model yourself. Generally? Use the functions Model:GetExtentsSize() and Model:GetModelCFrame() to create a relevant Region3 .

Like this:

wait(1)

local model = workspace:WaitForChild('Model') --path to any model

--model info
local size = model:GetExtentsSize()
local hsize = size/2
local pos = model:GetModelCFrame().p

--parameters for region
local lowp = pos - hsize
local highp = pos + hsize

local r3 = Region3.new(lowp,highp)

--optional warning box
local box = Instance.new('Part')
box.BrickColor = BrickColor.new('Really red')
box.Transparency=1
box.Anchored=true
box.CanCollide=false
box.CFrame = r3.CFrame
box.Size = r3.Size
box.Parent = workspace

--creating a manual ignore list is useful
local ignoreList = {}
--igore parts in the model
function fun(x) if x:IsA('BasePart') then table.insert(ignoreList,x) end end function scan(y) fun(y) for _,v in pairs(y:GetChildren()) do scan(v) end end scan(model)
--ignore parts such as baseplate
for _,v in pairs(workspace:GetChildren()) do if v:IsA('BasePart') then table.insert(ignoreList,v) end end

--in example:
while wait(1) do
	--most useful function!
	local parts = workspace:FindPartsInRegion3WithIgnoreList(r3,ignoreList,1000)
	if #parts>0 then
		box.Transparency=0.5
	else
		box.Transparency=0.9
	end
end