In the state of Tennessee, An off-duty police officer maintains his or her full arrest powers.

Opinion No. 02-002

OR, maybe:

There is no statute or rule of law in this state that places a mandatory duty upon police officers to keep the peace when "off duty." “To the contrary, when officers are ‘off duty,’ our statutes generally treat the officer as an ordinary private citizen and not as an agent or employee of the municipal police department under a general duty to keep the peace.”

UT County Technical Assistance Service: Off-Duty Status
White v. Revco Discount Drug Centers, Inc., 33 S.W.3d 713, 720-721 (Tenn. 2000).

Cambridge, MA:

IV. B.: Off-Duty Conduct While in the City: Given the fact that police officers retain their police powers regardless of their duty status while in the city, it is imperative that officers be mindful of their conduct both on and off-duty.

Off-Duty Police Powers & Conduct

North Carolina:

The rule in North Carolina is that an officer is almost never off duty even if they don't have the uniform on even if they are not in the police car they are on duty.

The outcome of the 1992 case shows the North Carolina court supports the conclusion that a police officer is always on duty.

The court states there is no distinction between on-duty and off-duty.

Can North Carolina officers arrest someone if they are off-duty?