Forum wouldn't let me format my above post, so I'll comment here...
The gist of 12028.5(b) is: When investigating domestic violence, any LEO acting in his official capacity may confiscate firearms or other deadly weapons found during legal searches if necessary for the safety of the alleged victim and/or officers.
OK, so an intelligent person would ask, "was it necessary for their safety?" Well, that's up to the court/jury to decide... if the accused bothers wasting time/money challenging the seizure. And if (s)he did try, I'd bet "the accused could post bail the same night and go home and murder the victim with that gun" would be enough to convince the jury.
Also, once a firearm is seized, even wrongfully, one has to usually get a letter from the DA or judge declaring it is not needed for evidence. One also has to pass DOJ screening before the weapon can be returned. The LEGR (Law Enforcement Gun Release) fee is $20+ (depending on the types and number of firearms).
ETA: It looks like AB 532 passed with flying colors, so as soon as the new law goes into effect, merely being detained/investigated for domestic violence is grounds for issuance of a warrant to search/seize all firearms believed to be possessed or under the person's control.
FYI, this only makes things slightly worse than they already are, since currently they can "request" surrender of all firearms owned by the suspect if a EPRO (Emergency Protective Restraining Order) is issued. To the best of my knowledge (direct experience and research) an EPRO can be issued via phone by a judge, and the suspect can be verbally 'served' if the paperwork is not immediately available.
So, in reality AB 532 only would allow them to search for unregistered weapons, plus get a free look inside your house for anything else illegal.