You do NOT need physical access to the car to hack it. See https://www.youtube.com/watch?v=MK0SrxBC1xs This is a hack of last year, so i hope that the demonstrated security hole has been fixed in the mean time.
What is worse is that the documentation for adding both physical keyfob (aka marrying them) and remote access keys (think license keys) are widely publicly available and the procedures are ridiculously easy. They are even demonstrated on youtube, talk about making it easy for potential thieves.
And one of the procedures for adding a new physical keyfob to the pool of stored authorized keys only takes about 3 seconds. After which you simply can lock the car and then unlock it with the newly married key, after which the alarm will shut off because you have unlocked the car with a valid key; and off you go - with the car.
Does anyone believe the police will be called for a car of which the alarm has been sounding for such a short period? Even the owner or the neighbours will probably think it was just a false alarm.
And even when the bugs in the security system are reported, the reaction is not to fix it, but to bury the existance of it: http://www.dailymail.co.uk/sciencetech/article-3201564/Hackers-reveal-flaw-100-cars-kept-secret-Volkwagen-TWO-YEARS-Bug-used-unlock-Kia-Lamborghini.html
Even when they 'fix' it, it is only implemented in the newly build models and never retrofitted in the already sold cars. If those cars are stolen, to bad for their owners. The manufacturers / car salesmen have your money and they are not going to spend a single cent of it to prevent your car from getting stolen because they made a faulty / vulnerable product in the past.