The US Patent and Trademark Office has granted Apple a patent for a curious accessory for the iPhone, iPad, MacBook and other devices. This is an external flash that can be connected via the Lightning interface or wirelessly.
According to the authors of the invention, the additional flash should fire simultaneously with the flash built into the mobile device.
The mobile device can output a control signal that includes information about the external flash and the status of the built-in flash, for example, to synchronize their pulses.
The control signal can be provided as an output signal from a single data pin in the port used for communication and for charging. It can include pulses separated in time, allowing the status of the built-in and external flash to be communicated.
Apple is not limiting flash use to iPhones only. Other devices are listed in the patent.