The North Carolina pre-arrest test gives a person the opportunity to submit to a chemical analysis before any arrest or other charge is made for DWI. Under NC GS 20-16.2(i), once a person who is stopped or questioned by a law enforcement officer investigating whether the person committed a DWI, the person may request to have a chemical analysis of their breath. The law enforcement officer must transport the person to the place where the chemical analysis is to be administered, confirm the request in writing, and administer the pre-arrest test.
The pre-arrest test is primarily useful for people who know they're not violating any implied-consent offenses and want to clear themselves before being arrested. Once transported to the place where the chemical analysis is to be administered, the person does not have to agree to take the chemical analysis. The officer may, however, charge you with any offense for which he has probable cause if you fail to comply fully with the test procedures. If you do take the pre-arrest test, the results will be admissible in evidence and used against you in any implied-consent offense that may arise.
Pre-arrest tests are very rare. Usually, the only people who request such tests are attorneys or those who have previously been charged with DWI. The benefit for the driver is that they are able to clear any DWI suspicions so there won't be charges on your record, delay or confuse testing procedures, and/or minimize the ability to for the officer to develop probable cause. Given that pre-arrest test requests are rarely made, the chance that the police will violate your rights is much higher.