California Code, Code of Civil Procedure - CCP § 2094

(a) An oath, affirmation, or declaration in an action or a proceeding, may be administered by obtaining an affirmative response to one of the following questions:

(b) In the alternative to the forms prescribed in subdivision (a), the court may administer an oath, affirmation, or declaration in an action or a proceeding in a manner that is calculated to awaken the person's conscience and impress the person's mind with the duty to tell the truth. The court shall satisfy itself that the person testifying understands that his or her testimony is being given under penalty of perjury.