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 read data from the Raspberry Pi.
Note
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.