Lights, audioand cameras.

Thin LED strips are pushed into the seams along the dash and door panels, and sometimes into the footwells, with the strip tucked behind the edge of the trim. Most kits change colour from a remote or a phone app. A line of light also makes scratches and fading on the panel next to it easier to see, so worn trim is worth cleaning up or replacing first.

The camera usually goes high on the windshield behind the rear-view mirror, out of your line of sight, and some kits come with a second camera for the rear glass. Its cable runs under the edge of the roof liner and down the pillar trim, then gets wired to the fuse box or plugged into the power socket. Memory cards wear out, so check now and then that it's still saving footage.

The factory stereo comes out and an Android touchscreen goes into the same slot, usually in a frame made for that model. On some cars the steering wheel buttons or the climate controls work through the old stereo, and whether they keep working afterwards depends on the car. Once it's in, you can use it for maps and music, and it can show a reverse camera.

A reverse camera sits near the number plate and puts the view behind the car on the dash screen as soon as you select reverse, so a car without a screen needs one fitted as well. A 360° system adds cameras at the front and under both mirrors. It combines the pictures into one view from above, and it has to be calibrated after fitting so they line up where they meet.

Each sensor sits in a hole drilled through the bumper, and a buzzer inside the car beeps faster as you get closer to a wall or another car. They can still miss a thin pole or a low kerb. If the bumper already has paint protection film, the film gets cut at every hole, so when you're planning both it's better to fit the sensors before the film goes on.

An upgrade usually starts with the door speakers and can go on to tweeters up on the dash and an amplifier under a seat or in the boot. While the door panels are off, the inside of each door can be lined with damping sheet. It cuts down rattles at high volume and takes out a little road noise too. How far it's worth going depends on what you listen to and how loud you like it.