If there is no power to the car, the ignition cylinder will 'eat' the key, refusing to allow the key to become ejected. This can happen when the battery has died or if a battery cable is loose. The battery is stored in the trunk, which can only be accessed by the key (which is now stuck in the ignition cylinder), or by the trunk release when the car has power. There is no other way of accessing the trunk as the seat release is also in the trunk. The only way to resolve this issue is to boost the car or to have a secondary key available to open the trunk (in the case of a loose battery cable).