The 3.5 mm TRRS connector for the headphones is located on the top left corner of the device for the first five generations (original through 4S), after which time it was moved to the bottom left corner. The headphone socket on the first-generation iPhone is recessed into the casing, making it incompatible with most headsets without the use of an adapter. Subsequent generations eliminated the problem by using a flush-mounted headphone socket. Cars equipped with an auxiliary jack allow handsfree use of the iPhone while driving as a substitute for Bluetooth. The iPhone 7 and later have no 3.5 mm headphone jack, and instead headsets must connect to the iPhone by Bluetooth, use Apple's Lightning port (which has replaced the 3.5 mm headphone jack), or (for traditional headsets) use the Lightning to 3.5 mm headphone jack adapter, which is included with iPhone 7 up until iPhone X and plugs into the Lightning port. This adapter is available for purchase at several leading retailers.