GPS would be useless for a determined thief, be it by simply jamming the GPS/cell signal or a RF sniffer to locate the (cellphone/whatnot) transmitter in the car and destroy it. From what I see, your social network sanction would be the only feasible option.

You probably meant "expert thief". Somebody who had 10000+ hours of expertise. Somebody who risked to get caught while gaining that expertise.

There are not so many real expert thieves. That's why extended security measures do work: less experienced majority of thieves is caught outright, and more experienced minority of thieves is eventually caught due to unforeseen circumstances (unexpected witness, unexpected new security measure, etc.).

For example, GPS transmitter can stay silent until it gets "You are stolen" signal.

There could be more than one transmitter in a car. It may get activated only when on the move (and not in a garage) etc.

"For example, GPS transmitter can stay silent until it gets "You are stolen" signal."

That's true, but most electronic circuits emit stray radiation, switching or crystal references. Not only that, the hypothetical receiver needed for your stolen signal has a least a local oscillator with a nice and probably almost on clean signal. (I think in UK they used something like this to track people that didn't pay their TV tax, or even SS tracking WWII French resistance, but it might be an urban legend, although feasible, since stray LO frequency can propagate to the antenna and is sometimes used to check correct mixer/filter tuning).

Or even more simple, get a big truck with metal cage for RF shielding and disassemble the car for parts, which is more profitable. They just need to get rid of serial numbers and such.

I agree about the expert thief, but considering that [internet] criminal gangs go to the trouble of hiring experts to do the (hard) technical part, I would guess that gangs interested in stealing expensive cars would have no problem finding unscrupulous people to help them disable any security measure.

Even the car share company devises a security measure, what stops someone from registering into the service with fake ID and knowing all about it to neutralize it?

Why would a person who was able to pass background check and has security expertise - risk his safe life and good income by dealing with criminal gangs?

Yes, it's possible, but as an exception, not as a rule.

Criminal activity would never stop completely, but not because it's impossible to beat criminals, but because as soon as crime goes down - people and businesses start doing more risky activities, trust more and check less.

> I think in UK they used something like this to track people that didn't pay their TV tax

There is a certain amount of evidence to suggest that the TV detector vans are (if not entirely fictional) exist mostly to scare people into paying.

Yea but it only takes one expert thief to tell his minions what to do.

You are overestimating the ability of people to listen to directions and think and adapt them for themselves.

If it were that easy, none of us here would be complaining about hiring incompetent people :)

> by only allowing rentals to people within two degrees of separation on a social networking site

Thereby increasing the chicken and egg problem ten fold

Not only that; what value is the middle man bringing in that situation, vs. "Hey, Bob, can I borrow your car for a while? Here's some cash."? Non-zero? Sure, but probably not enough to capture and survive on.