Serial data can also be sent through Bluetooth by connecting a HC-05 Bluetooth module that supports the Serial Port Profile (SPP) to the GPIO serial RX/TX pins. This allows the serial connection to become wireless, which allows Android tablets or smartphones to be used to control things and to read data from Raspberry Pi:
The HC-05 Bluetooth module for the TLL serial
While it is possible to achieve a similar result using a USB Bluetooth dongle, additional configuration would be required depending on the particular dongle used. The TTL Bluetooth module provides a drop-in replacement for a physical cable, requiring very little additional configuration.