Can police search my trunk?

The scope of a vehicle search depends on which exception the officer is relying on, and the exceptions have different reaches.

Probable cause to believe evidence is in the vehicle generally permits a search of anywhere in the vehicle that evidence could be — including the trunk and closed containers within it. But it's limited by what's being looked for. Probable cause to believe there's a stolen television doesn't justify opening a small envelope.

A search incident to arrest is much narrower. It generally reaches the passenger compartment, and only where the arrestee could access it or where it's reasonable to believe evidence of the arrest offense is there. That typically doesn't extend to the trunk.

An inventory search after impound can reach the trunk, but only if conducted according to standardized procedures rather than as an investigative search wearing a different label.