I call smart device a sensor or an actuator that includes its own MCU. The MCU acquires and processes the raw data provided by the sensor, performs the required calculations and delivers ready-to-use measures to the master.
A GPS is a good example. The GPS acquires the signal from different satellites, performs all the calculations and delivers the master with NMEA sentences with latitude, longitude and altitude, among other measures, through a standard serial port.
Those projects are shared with the fischertechnik Corner website, as most of the smart sensors are intended for the fischertechnik Robo TX controller. This section in more technical oriented.