How Does OnTriggerEnter() Work?

Hello everyone, the question I'm asking is probably more involved than the title would make it appear. Specifically, I'm asking how t$$anonymous$$s method (and its related methods) actually go about figuring out if an object has entered / remains inside / has exited a collider.

For example, I could use collider.bounds.Contains() to check if a point is inside a sphere/capsule/mesh collider, but since bounds is "just a box" the result may not be accurate at all. Yet, OnTriggerEnter() will give an accurate result. So I'm after what makes that method so accurate over somet$$anonymous$$ng like bounds.Contains(), or in other words, how to build my own method similar to OnTriggerEnter() / OnTriggerStay().

In my specific case, I'm trying to check if "objects of interest" are wit$$anonymous$$n some of my colliders when the "game starts", meaning that OnTriggerEnter() won't be called at all because the objects start inside the colliders, and bounds.Contains() isn't very accurate.

Any ideas are appreciated, thank you for reading.