Cal. PEN § 631

(a) Any person who, by means of any machine, instrument, or contrivance, or in any other manner, intentionally taps, or makes any unauthorized connection, whether physically, electrically, acoustically, inductively, or otherwise, with any telegraph or telephone wire, line, cable, or instrument, including the wire, line, cable, or instrument of any internal telephonic communication system, or who willfully and without the consent of all parties to the communication, or in any unauthorized manner, reads, or attempts to read, or to learn the contents or meaning of any message, report, or communication while the same is in transit or passing over any wire, line, or cable, or is being sent from, or received at any place within this state; or who uses, or attempts to use, in any manner, or for any purpose, or to communicate in any way, any information so obtained, or who aids, agrees with, employs, or conspires with any person or persons to unlawfully do, or permit, or cause to be done any of the acts or things mentioned above in 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 a fine and imprisonment in the county jail or pursuant to subdivision (h) of Section 1170. If the person has previously been convicted of a violation of this section or Section 632, 632.5, 632.6, 632.7, or 636, the offense is punishable by a fine not exceeding ten thousand dollars ($10,000), 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.

(b) This section shall not apply to any of the following:

(1) Any public utility, or telephone company, engaged in the business of providing communications services and facilities, or to the officers, employees or agents thereof, where the acts otherwise prohibited herein are for the purpose of construction, maintenance, conduct or operation of the services and facilities of the public utility or telephone company.

(2) The use of any instrument, equipment, facility, or service furnished and used pursuant to the tariffs of a public utility.

(3) Any telephonic communication system used for communication exclusively within a state, county, city and county, or city correctional facility.

(c) For purposes of this section, “telephone company” is defined in paragraph (3) of subdivision (c) of Section 638.

(d) Except as proof in an action or prosecution for violation of this section, no evidence obtained in violation of this section shall be admissible in any judicial, administrative, legislative, or other proceeding.