RF experts, random odd question

[rizla420]

This may seem like an odd questions, not sure on its BANNED.

Its possibly a new take on radar/police detection. Would it be possible to detect a police vehicle based on its RF signature. It seems like most moder police cruisers have some sort of radio link back to headquarters that they use to access RMV/DMV info. On top of that you have the regular police channels they use for radio'ing in etc

I'm wondering whether it would be possibly by analyzing the RF signals to determine whether there is a police car in the vicinity.

Why would i want to do this? eh, just curious to know whether something like this is even possible. A new take on radar detectors. Rather than relying on whether you see radar/lidar you see if there is a car that is putting out a bunch of different signals that you could within reason say "thats not normal, must be the fuzz. proceed with caution"

Anyhow just wondering if it someone else might have considered it and what the possible pitfalls to this approach would be.

[zener]

Yes of course you could do it but you need to know the frequencies they are using. Back in the day (20 years ago?) there was a thing called the CHiPs detector that would detect CHP repeater frequencies that were used in the cars. I don't know if such a thing would work anymore. The pitfall is I don't think it will do much about laser. Your best bet is don't speed, or get a good lawyer and have a lot of money.

[stephanie]

You can buy trunk-tracking scanners that let you program the local emergency services frequencies then you can listen in. Mod that with an attenuated antenna and you can use it to tell if an emergency services radio is transmitting in your vicinity. However it would be very geographically limited, i.e. the frequencies for your town / county won't be the same as the next one, so if you travel a lot through different jurisdictions it won't be much use.

And you can't just program it for any possible police frequency as then it could trigger false positivies, i.e. a police frequency from two towns over, might be in use by the local telephone repair company in this town.

I suppose you could tie sets of frequencies against geographical areas then use a GPS to sort out what frequencies to listen to based on where the sensor is located, but even after all that, it's still only going to be triggered if someone transmits on one of the frequencies when the scanner happens to be listening to that frequency. Police vehicles wouldn't be constantly emitting RF, even their terminals only transmit when there's actual data to be sent. And then it's usually a short burst of packet data.

As an alternative method, how about using optical sensors to detect flashing lights?