Like many other states, California has an implied consent law which provides that drivers have consented in advance to submitting to a BAC test should they be pulled over on suspicion of drunk driving. Police can give a driver a chemical breath test at the scene and the results can be used as evidence against the driver.
It's hard to talk about domestic violence. Victims often don't want to talk about it, but they deserve to be heard. The people accused of committing domestic violence may not want to talk about it, but they deserve a defense.