This accessory is apparatus capable of implementing a method that can affect one or more features of a portable electronic device when brought into a vehicle having a radio with a right and left speaker. The accessory has a sender for initiating transmission of an RF test signal at the portable electronic device. The RF test signal is arranged to cause the radio to produce a distinct pair of audio responses from the right and left speaker. The accessory has a discriminator for determining for the right and left speaker the corresponding return delay between transmission of the RF test signal and arrival of the distinct pair of audio responses at the portable electronic device.