California Code, Labor Code - LAB § 3358

Watchmen for nonindustrial establishments, paid by subscription by several persons, are not employees under this division.  In other cases where watchmen, paid by subscription by several persons, have at the time of the injury sustained by them taken out and maintained in force insurance upon themselves as self-employing persons, conferring benefits equal to those conferred by this division, the employer is not liable under this division.