It seems that Getaround might actually be preferable to traditional car rental methods because of the low friction associated with the transaction. Enterprise Rent-A-Car will pick you up, but you have to go back to the retail location to fill-out paperwork and drop off the kid who brought the car to you. It would be so much easier to just use a car already located in your building's parking garage.
I looked at the Getaround site and couldn't find any details about how the in-car gizmo works. This support thread has some clues:
http://support.getaround.com/discussions/questions/8-power-f...
I'm a bit bothered by the statement "without giving too much away..." Security through obscurity? I presume that the CarKit does not integrate with the vehicle ignition? If not, must a person who rents his vehicle leave an ignition key in the vehicle? If so, the iPhone app implicitly becomes a location tool for easy-to-steal vehicles. Just smash a window and start up the car. If the carkit does indeed replace the need for a physical key, I suppose the security concerns would be no worse than those associated with aftermarket remote starters. It is bothersome that Getaround is not more forthcoming about the technology.