This is a post from another part of the board. Thought it might be useful - Rick
The detectors will work under many fairings (that's where I put mine). Not only do DC and VA frown on them, but they're thief bait too.
Testing it -
You do need to test it, though. Put the detector in the car, and find a supermarket or store where your detector goes off. Find a parking lot at the edge of where you can detect the store's door openers. Then, take your bike to that lot. Hold the detector under different parts of the fairing, and see if the range is affected greatly. If you just lose a little bit, it's No Big Deal. If you lose a lot then beware. Also, make sure you try several positions under the fairing; there's often metal where you don't expect it.
Hearing it -
The helmet alerts don't do anything for me; I don't need to be reminded what gear I'm in or where the RPMs are.
I would choose one of these detectors:
RX65 - I may be going to this one, because it has voice alerts (You can get the earbud type speakers and the alerts in your helmet).
Escort 8500 x50 - you can buy a set of LEDs http://www.marcparnes.com/Visual_Alert.htm that plug into the audio jack, and can be mounted in your line of sight.
V1 - I have this, I like the performance, but it's large, and all phone wires for the remotes make them very noticeable. It can also be used with the visual alert.
Finally, the earbud speakers can be used instead of earplugs, but ditch 'em if you get pulled over in MD! You can also take off the foam on the earplugs, and replace the foam with a regular set of foam earplug (with a hole burned through the center) to give excellent hearing protection. Don't use this for music, though, or you'll never hear things like sirens, airhorns, and other important stuff.
May you ride often and well,