Simply Auto FTBC1 Bluetooth Car FM Transmitter and ChargerPlenty of cars on the road have a perfectly good radio and no way to connect a phone to it. Simply Auto Bluetooth FM Transmitter plugs into the 12V socket and bridges that gap, sending audio from your phone to the car's FM radio so music, podcasts and navigation prompts come through the car speakers.Calls work the same way. Pair the phone over Bluetooth 5.0 and incoming calls switch the unit automatically from music to call mode, so you can answer without touching the handset.It charges at the same time. Two USB ports and a USB-C port between them cover most phones, tablets and accessories, and a MicroSD slot plays music straight from a card if you would rather not use the phone at all.A built-in voltmeter shows the car's battery voltage on the display. This is extremely useful, particularly on a car that sits for long periods, since a battery dropping below its normal resting voltage tends to give notice before it leaves you stranded.Seven LED colour modes let you set the display to suit the interior, and the rubberised finish resists the cracking and chipping that plastic adapters develop over a few summers in a hot car.Getting the best from it: FM transmitters work by broadcasting on an unused radio frequency, so the quality you get depends on finding one that is genuinely clear. In towns and cities the FM band is busy, and it is worth trying several frequencies before settling. The lower end of the band, around 87.5 to 88 MHz, is often quietest. Retune if you notice interference creeping in on a longer journey, since a frequency that is clear in one area may not be in the next.