This article is from the California Driving (and Surviving) FAQ, by "George J Wu" firstname.lastname@example.org with numerous contributions by others.
from email@example.com (Chuck Fry) on 30 Jul 92:
They're perfectly legal. I think it's a combination of factors that
keeps their popularity down.
First, there seems to be a mistaken impression that the CHP is not
permitted to use radar. This is false; although for years the
Legislature shot down funding for radar equipment, local jurisdictions
have always been free to provide gear to the CHP for local trouble
spots, and I believe the CHP now has funding to buy a limited number
of radar units of their own. And remember that local police and
sheriff's deputies have never been reluctant to use radar.
Second is the fact that radar is essentially useless in heavy freeway
traffic, because there's no way to pinpoint one violator. And at rush
hour, much of this traffic doesn't ever see the speed limit anyway.
Third, I just don't think Californians have as much of an adversarial
relationship with police as residents of other states do. The CHP by
and large plays fair, and as a result most drivers here seem to feel
they deserved a ticket if they got caught.
I carry a radar detector and make frequent use of it, especially in
known radar speed traps (e.g. most of Palo Alto especially Alma St.
and Charleston, highway 17 through the mountains). I highly recommend
a good radar detector to anyone who drives, whether your foot is made
of lead or feathers, since most urban speed limits in California are
set well below the 85th percentile speed and are thus de facto speed
from firstname.lastname@example.org (George Wu) on 5 Nov 96:
CHP has used radar for years on Highway 17. They've recently added
it to Highway 85 south of Mountain View due to a spate of recent head
on collisions across the median strip.