California Code of Regulations 978.20(a) dictates that you have to have a non rapidly-detachable magazine on your AR15. The magazine must require a tool to release it. The Bullet Button is a drop-in replacement for the factory button that prevents your magazine being removed without the use of a tool and thus assists in making your AR compliant. The Bullet Button can be installed in minutes.
Purchase an Assault Planet Bullet Button at Brownells, a name you can trust.