MP3 players such as Apple’s popular iPod have revolutionised the way we listen to music, but the technology was slow to come to cars. The result is that most of us have to pay to play our favourite songs through our vehicle’s sound system.

The cheapest route to MP3 in your car is an FM transmitter. Made legal late last year, they broadcast a low-power radio signal which is picked up by the in-car tuner. Most are made for the iPod, and our winner had to charge the player, as well as transmit clearly via user-friendly controls.