Radios are devices that are capable of transmitting signals through electromagnetic waves with frequencies. These frequencies and electromagnetic radiation travels through air and space. Once the electromagnetic waves and frequencies are being transmitted, it can be transformed into sounds. The transmitted sound can carry information.

An AM-FM Radio is a device that sends music and voice in Medium Frequency. The AM broadcast radio works by modulating the amplitude of transmitted sound to be in proportion with the sound amplitude captured by a microphone. In this process, the transmitted frequency is unchanged. While in FM broadcast radio or frequency modulation, transmits sounds in a very high frequency (VHF). This makes the FM broadcast radio send sounds with higher definition than AM radio. 

There is also a Two-way radio, a device that is capable of transmitting and receiving sound or voice at the same time. This device is also referred as a transceiver. Functionalities of a Two-way radio are also offered in mobile phones, cellular phones and-held radios (walkie-talkies). This device uses two different radio frequencies that can transmit signals at two different directions. This allows its users to have their conversations simultaneously. 

A WiFi Radio or also known as the Internet Radio is a type of radio that receives frequencies that are broadcasted over the internet.  WiFi Radio is capable to receive any radio station as long as the station is connected to the Internet. Over 20,000 radio stations are broadcasted over the Internet, both AM and FM. WiFi Radio was created with different modules. It requires an Internet connection, codec used in streaming the data, amplifier and speaker.

Other radio devices also includes the Shortwave radio, a radio that is only capable of transmitting sounds in a high frequency range of 3,000 kHz up to 30,000 kHz. There is also the Emergency Radio, a device that only receives sound frequencies in case of power shortage. This kind of radio is also useful when it comes to transmitting radio signals or standard AM-FM stations in remote places. This device was designed to operate on minimal power sources. The Emergency Radio is mostly supported by a Weather Radio service. Weather radio is a service that broadcasts weather-related announcements. This service may also broadcast other emergency announcements which include natural disasters, child abduction alert bulletin, and terrorist attacks. This service uses a very high frequency (VHF) with radio frequency scanners.

Advance radio technology such as the Satellite radio uses a digital radio signal. The Satellite radio or also known as the subscription radio is capable of receiving radio signals through a communications satellite. The Satellite radio can cover and provide services in a wider geographical range. This kind of technology provides functions to some mobile services that allow its users to listen to radio stations anywhere across the continent. Another advance innovation on the technology of radio signals is a system called HD Radio. The HD radio technology enables AM-FM stations to transmit audio data digitally with the use of analog signals. This allows both AM and FM stations to broadcast within a same channel. This service also provides a function that can add new FM channels with inputted text information.