How does in_array check if an object is in an array of objects?

Does in_array() do object comparison where it checks that all attributes are the same? What if $obj1 === $obj2, will it just do pointer comparison instead?

I'm using an ORM, so I'd rather loop over the objects testing if $obj1->getId() is already in the array if it does object comparison. If not, in_array is much more concise.