If your car doesn't come with TV sets installed in the front-seat headrests for back-seat viewing, you can install such TV sets yourself. You will have to cut holes into the headrests to install the TV, which could void you car's warranty. And this might be best left to a professional at an electronics store or auto bodyworks garage. A full headrest TV set should come with the TV itself, the frame it rests in, an audio/video console and the wires to connect everything.
Remove the headrest from the car seat. Remove the upholstery cover from the headrest to reveal the foam cushioning underneath. Trace the edge of the TV frame on the rear side of the foam with a permanent marker.
Cut into the foam with a razor knife, digging it to the same depth as the TV frame. Cutting the foam out in pieces may help. Place the frame into the hole to test how well it fits. Remove the frame and whittle away the foam until the frame can fit securely in the foam.
Apply contact cement along the inner bowl of the hole and the outside ends of the TV frame (not the inside of the frame, where the TV fits). Place the frame in the hole while the cement is wet, wait for the cement to set and push the frame to fully stick it inside the hole.
Locate the hole in the frame where the TV's cable will go through. Poke a hole through the foam all the way to the headrest front, using a large screwdriver, so the cable will be able to go through it.
Slip the upholstery back on the headrest. Cut away the upholstery where it is over the hole. You can use more contact cement to glue the upholstery edges to the edges of the frame.
Place the TV screen into its frame. Make sure all contact cement has dried and hardened before you do this. Send the cable through its exit hole and through the headrest foam, then store it near the bottom edge of the upholstery so it can connect to the A/V wires.
Connect the TV to its audio/video console. This box connects peripherals like headphones and an external DVD player. This box can be stored underneath the front seat and the cable connecting it to the TV can run under the seat's upholstery.
Connect the power source cable to the console. This can be a plug into the car's lighter adaptor, or it can connect directly to the car battery. The kit should have all the instructions on how to wire the connections.
A TV with a 7-inch screen or smaller works best. This is especially true of small cars like the HHR or the PT Cruiser.