if by chance you managed to lock yourself out of your car,could you unlock it by phoning your house(where presumably a spare key is)and getting someone to depress the "open" button of the spare key fob over a mobile that would be recognised by the car sensor? obviously only would work on modern cars with sonic key fobs,but is it possible??

No. It's been discussed a month ago.

1. Modern keyfobs are radio emitters - not sonic.

2. Even if keyfobs were sonic, they don't emit an audible tone - it's either sub or ultrasonic, ie outside the frequency range of the microphone of the cellphone, which is restricted by internal filters to a band of frequencies in the range of 300 to 3000 Hertz (hz).
Any sound below 300hz or above 3000hz would not be transmitted by the phone.

However, if your car is equipped with "OnStar", as are some GM products in the U.S., you can make a phone call and have your car unlocked electronically. An expensive advantage you might use once in the life of the car.

no, but if you are standing out of range from your car and you forgot to turn it off you can put the lock agianst your head and it will turn off