A modular portable device system and method allow extended user input. The system includes a first device and a second device, the devices being attachable via a plurality of magnetic attachment points (magnets or magnetically responsive attachment points) on each. In a first configuration, the devices are held together by all of the magnetic attachment points, and in this configuration an extended user input facility on the second device is not user-accessible. In a second configuration, the devices are connected by only a subset of the magnetic attachment points, and in this second configuration the extended user input facility is user-accessible. A Hall Effect sensor on the first device and sensor magnet on the second device are positioned to overlap when the devices are connected in the second configuration in order to alert the first device that the second device has been attached in the extended input mode.