Even though the main way Bluetooth devices connect with each other is through frequencies, there is some hardware that goes along with it.
You can easily add bluetooth to any device by adding a USB dongle with the hardware already set up
It requires a transmitter and receiver and control chips
Every Bluetooth device has two main aspects: a baseband controller and a radio
There are three classes of Bluetooth devices:
Class 1: These are usually modules you can add on to larger devices and have the ability to reach 100 meters. Max permitted power is 100mW.
Class 2: These are the most common bluetooth devices such as headphones or speakers. The max permitted power is 2.5mW.
Class 3: These are designed for extremely short-range connections of about 1 meter or less. Max permitted power is 1mW.
You can implement Bluetooth in multiple ways, but the three main ways are:
Integrated Single-chip: baseband circuits and Bluetooth radio are completely integrated into the host SoC module. Most commonly used in headsets
Standalone single-chip: a single Bluetooth SoC containing the baseband and radio is integrated into a larger system. This is commonly seen in mice, keyboards, or even smartphones
Dual-chip: the baseband and radio are in two separate chip packages. This technique isn’t used as often as either of the single-chip techniques