> You would not get a search warrant [for several unlocked cars]

Hold up, you state that rather firmly but what's the reasoning that supports it?

What's the rationale that separates 1 car from "several" for probable cause?

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I feel there's a risk of conflating:

1. Good reason to believe X is somehow involved a crime.

2. Probable cause to search for/inside something owned by X.

While there is a strong correlation between the answers to those two questions, they are definitely not the same.