How can I detect if a player is near (as an event), possible? Without using while true do?

I don't believe there's an event for this, but you can use a loop and if creating a new thread is necessary, coroutines. You can use magnitude to check the distance between two specified parts. For example:

local base = workspace.base
local part = workspace.part
coroutine.resume(coroutine.create(function()
while wait(1) do
print (part.Position - base.Position).magnitude
end
end))
print("bork")

You can make an invisible non can collide-able cylinder/sphere and when a player touches it with the touched event you can change a variable to true. When the player leaves the range of nearness (invisible cylinder) you can use the touchended event and change a variable to false. Ex

--Put this script in an invisible non can collideable sphere that surrounds the object that you want to know if the player is near

PlayerIsNear = false

script.Parent.Touched:connect(function()
PlayerIsNear = true
end)

script.Parent.Touchended:connect(function()
PlayerIsNear = false
end)

if PlayerIsNear == true then
--Do whatever you want here

This creates a lot less lag then a loop

There isn't an event, but if you want an alternative method, you can use magnitudes to detect how close the player is to an object. From there you can determine what you want to do with the script. I used this to create a type of radar/ way to find players near you.