HiLetgo HC-05 Wireless Bluetooth RF Transceiver Master Slave Integrated Bluetooth Module 6 Pin Wireless Serial Port Communication BT Module for Arduino

The factory setting is slave mode, but you can set this module to master mode so that you might be able to connect to other Bluetooth 2.0 devices. HC-05 Wireless BT Module
HC-05 Wireless BT Module: with this HC 05 Bluetooth module, You can quickly add the Bluetooth feature to your Arduino project, and then you can use your android phone to control some gadgets, such
as: switch, LED.
Master and Slave 2-IN-1 HC 05 Module: Working Voltage 3.6V to 6V, Default
baud rate: 9600, Default pin: 1234
Button: Press the button, the module enter the AT mode. AT commands are executed only in AT mode.
6 PIN Dopunt Cable: with this Dupont Cable, you can easily connect this HC-05 Bluetooth module to your Arduino Board