is simply inserted in the cassette player like any cassette, set on play, and music from a Bluetooth device like a mobile phone or laptop can be played through the cassette player. A common alternative to cassette adapters is FM transmitters. These devices often require external power and convert the device's electrical signal into radio waves which are then transmitted over an unused FM frequency to a nearby FM tuner. The cassette adapter is usually considered superior as it is much less prone to interference. Applications A cassette adapter could also be used with other audio equipment, such as a microphone, handheld game console, or laptop computer. It can also be used in a home tape deck to play sound from any equipment, such as a personal computer, when computer speakers are in short supply. Hands-free cell phone, where a microphone and aux cable are connected to the cassette tape which broadcasts the audio from the call to the car's speakers CD player (the original application for cassette adapters) FM radio HD radio (for the large numbers of receivers that do not natively support this broadcast standard) Laptop computer Portable media players (iPod, MP3 player, Zune) Mechanism A cassette adapter is shaped like a cassette tape. However, instead of having reels of tape inside, it has a transmitting head where the tape is normally read by the reading head. This transmitting head is connected to the input cord, which connects the head to the audio source. A cassette adapter must also include a mechanism that simulates tape movement. Modern cassette players monitor tape movement to detect when the tape ends. This is done using a rolling wheel that rides against the tape. To simulate tape movement, a system of gears or a drive belt connects the tape player's drive motor (via the take-up spindle) to a wheel inside the adapter. This wheel rides against the detection wheel to simulate tape movement. Because the wheel never stops spinning, the deck never senses an end-of-tape and never tries to reverse the tape. Some adapters contain a one way locking mechanism, to stop the detection wheel if the tape is played in the wrong direction (and thus reading the wrong side of the head). The stopped wheel then would cause the cassette player to either stop the tape, or reverse the direction if the player supports it. See also FM transmitter (personal device)