This is false. It's an old fundraising claim used by the ACLU; they have since set up pages backing away from it (because convincing people in the US that they don't have rights they do in fact have is not good civil liberties advocacy). There's direct SCOTUS precedent on this.

There's a 100 air mile border definition that's material to immigration enforcement (with complicated limitations). It does not determine where searches under the border search exception can occur.