If you lock your keys in the car and the spare keys are at home, call
someone at home on their cell phone from your cell phone.
Hold your cell phone about a foot from your car door and have the person
at your home press the unlock button, holding it near the mobile phone on
their end. Your car will unlock. Saves someone from having to drive your
keys to you. Distance is no object. You could be hundreds of miles away,
and if you can reach someone who has the other "remote" for your car, you
can unlock the doors (or the trunk).
mind