Pen. Code, § 638.51

(a) Except as provided in subdivision (b), a person may not install or use a pen register or a trap and trace device without first obtaining a court order pursuant to Section 638.52 or 638.53.

(b) A provider of electronic or wire communication service may use a pen register or a trap and trace device for any of the following purposes:

(1) To operate, maintain, and test a wire or electronic communication service.

(2) To protect the rights or property of the provider.

(3) To protect users of the service from abuse of service or unlawful use of service.

(4) To record the fact that a wire or electronic communication was initiated or completed to protect the provider, another provider furnishing service toward the completion of the wire communication, or a user of that service, from fraudulent, unlawful, or abusive use of service.

(5) If the consent of the user of that service has been obtained.

(c) A violation of this section is punishable by a fine not exceeding two thousand five hundred dollars ($2,500), or by imprisonment in the county jail not exceeding one year, or by imprisonment pursuant to subdivision (h) of Section 1170, or by both that fine and imprisonment.

(d) A good faith reliance on an order issued pursuant to Section 638.52, or an authorization made pursuant to Section 638.53, is a complete defense to a civil or criminal action brought under this section or under this chapter.