I have a thought. There are already services that attempt to do this, with the exception that they do not automate the reporting: http://www.trapster.com/
Radar detectors are very finicky, and my understanding is that it is difficult to build a reliable one.
Now, my experience is with a specific model (and I think a very very popular one, the Passport 9500), it has an RJ45 connection which plugs into the unit and then the other end plugs into your car cigarette lighter for power. The end which plugs into your car cigarette lighter has a dongle and LED which flashes when radar has been detected (along with a mute button). There is two-way state information transmitted over the line in addition to power.
It would be awesome to build a "man in the middle" device to intercept and interpret the signals from popular device models, then send it's own signal to the iPhone/Android/WP7 phone to share the information.
This has the large benefit of being extremely cheaper to manufacture. Additionally, you're leaving the challenge of building the actual Radar Detection to well established companies who know what they are doing.
Additionally the service could look for patterns in the data. False positives are a huge problem with detectors. When every car is reporting radar 24/7 at this one location, you know it's most likely a false positive. Newer Passport models have this logic built in with GPS.
> Additionally, you're leaving the challenge of building the actual Radar Detection to well established companies who know what they are doing.
This is probably going to become more and more important in future. Both RF and processing electronics are becoming cheaper and more capable - and this will lead to 'smarter' radar technology being affordable in speed-gun type devices. Old-school dump pulse-doppler systems are trivially easy to detect, but there are many radar technologies out there that will present a much bigger challenge. It wouldn't surprise if we soon see PCL (passive coherent location) based speed traps soon. Passive radars like these can use radiators of opportunity (cell towers, TV, FM radio) and don't need to emit any energy of their own. They aren't undetectable, but are much harder to detect.
The point is that radar detection is going to become much harder in future, and while the equipment will probably still get cheaper, the technical sophistication required for detection will increase.
> You cannot passively detect another passive receiver.
In general, there isn't really such a thing as a passive receiver. The typical radar receiver design will downmix the incoming signal to some lower frequency (IF) using its 'local oscillator'. Some of the energy from this oscillator will leak out of the receiver and be detectable. This is only one of several possibilities for detecting receivers.
So no, not undetectable, but much harder than detecting an active transmitter.
Are you joking ? How do you distinguish this "leaked oscillation" coming from radar-detector from all other pieces of electronics your car is stuffed up with ? Say, from your car stereo ?
Radar detectors are very finicky, and my understanding is that it is difficult to build a reliable one.
Now, my experience is with a specific model (and I think a very very popular one, the Passport 9500), it has an RJ45 connection which plugs into the unit and then the other end plugs into your car cigarette lighter for power. The end which plugs into your car cigarette lighter has a dongle and LED which flashes when radar has been detected (along with a mute button). There is two-way state information transmitted over the line in addition to power.
It would be awesome to build a "man in the middle" device to intercept and interpret the signals from popular device models, then send it's own signal to the iPhone/Android/WP7 phone to share the information.
This has the large benefit of being extremely cheaper to manufacture. Additionally, you're leaving the challenge of building the actual Radar Detection to well established companies who know what they are doing.
Additionally the service could look for patterns in the data. False positives are a huge problem with detectors. When every car is reporting radar 24/7 at this one location, you know it's most likely a false positive. Newer Passport models have this logic built in with GPS.