Businesses in the car radio category supply, install, repair or upgrade audio and radio equipment for cars and other vehicles. This can include standard replacement radios and head units, DAB and digital radio receivers, aerials, amplifiers, speakers and subwoofers. Some also fit Bluetooth connectivity, auxiliary or USB inputs, smartphone integration and hands-free systems, allowing drivers to play audio or make calls through the vehicle's audio equipment. Installation may involve checking that a unit is compatible with the vehicle, connecting it to the existing wiring and aerial, and retaining features such as steering-wheel controls or factory displays where possible. Specialists may diagnose faults including poor reception, loss of sound, damaged wiring or equipment that will not switch on, and carry out repairs or replacements. Depending on the business, services can also extend to audio upgrades, security features and integrating newer equipment with a vehicle's existing systems.