According to the California CHP website, no sound metering devices are needed to issue tickets:

"New law (27150.2 VC) does not require law enforcement to use sound level meters to test for excessive noise. Citation is based on officer's judgment. Cited violators may have testing done at smog referee stations or may be directed by the court to have testing done. Vehicles in violation must be brought into compliance. A fine may also be imposed."

 

OK, my buddy went to the DMV Saturday. The guy asked if he had aftermarket pipes, he said yes, the guy said ok, then their illegal.

He asked the guy if he was going to check the decible noise or not, the guy told him to start the bike up, drive around the parking lot so he could hear it.

The DMV guy told him he wasn't going to waist his time checking it because he could tell it had baffles in it, case closed.

So now he made a copy of the DMV form to carry with him, he's happy.