[The car is not a ḥirz (protected place of safekeeping) for what is placed in it]

The answer – and Allah is the One who grants success – is that what appears to me is that the car is not a ḥirz for what is placed in it, whether its doors are locked or unlocked.
The proof of that is that the car itself, if it is stolen from within a ḥirz, the thief’s hand is cut; but if it is stolen from outside its ḥirz, the thief’s hand is not cut. This is what the evidences entail, and it is the madhhab, as stated in al-Azhār and its commentaries.
And whatever is in itself a thing that is kept in a ḥirz does not become a ḥirz for something else; and this is what the scholars of the madhhab have said regarding the bag, the sack, the chest, and the like of that.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2