Cal. Code of Civil Procedure § 415.45

(a) A summons in an action for unlawful detainer of real property may be served by posting if upon affidavit it appears to the satisfaction of the court in which the action is pending that the party to be served cannot with reasonable diligence be served in any manner specified in this article other than publication and if either of the following conditions exists: (1) A cause of action exists against the party upon whom service is to be made or they are a necessary or proper party to the action. (2) The party to be served has or claims an interest in real property in this state that is subject to the jurisdiction of the court or the relief demanded in the action consists wholly or in part in excluding such party from any interest in such property. (b) The court shall order the summons to be posted on the premises in a manner most likely to give actual notice to the party to be served and direct that a copy of the summons and of the complaint be forthwith mailed by certified mail to such party at the party’s last known address. (c) Service of summons in this manner is deemed complete on the 10th day after posting and mailing. (d) (1) For purposes of this section, a party shows reasonable diligence by attempting personal delivery of the summons and complaint, in good faith, on at least three occasions on three different days at three different times. (2) Except with respect to actions for unlawful detainer of “commercial real property,” as defined under subdivision (d) of Section 1161.1 or “program participants,” as defined under paragraph (9) of subdivision (a) of Section 6205.5 of the Government Code, at least one of the attempts shall be made at the dwelling place or usual place of abode of the person to be served, provided that the dwelling place or usual place of abode is known or could be determined with reasonable effort. (e) Notwithstanding an order for posting of the summons, a summons may be served in any other manner authorized by this article, except publication, in which event such service shall supersede any posted summons. (f) This section shall become operative on January 1, 2027.