AmericanSecurityCo.com has backup sensors for cars of all makes. These sensors are placed in the trunk somewhere and will allow a user to see what is behind them through a monitor. The ones that are built into the cars work just as well as the ones that are added.
As long as these sensors are professionally installed by someone who knows what they are doing, they will work just fine. They are kind of like hidden cameras that are placed in key chains and all kinds of products. They are very small and are usually embedded into a trunk light or a trunk keyhole. This makes them so sleek and high profile that people like them on their cars. If they had to become an entire camera mounted to the rear of the vehicle, most people would opt to leave them out. They are pretty easy to connect to the front as well.
If someone has experience installing any sort of stereo system in a car, it is pretty much the same concept. There needs to be a wire that runs from the trunk to the stereo and monitor in the front of the car. This is usually run underneath the car mats and then up the dashboard. The wire is fairly thin and it should be an easy connection. It is important that this is installed before the stereo is installed completely though. This will prevent the need for the person to rip the stereo out more times than they would like. This can cause several problems.
If the stereo or monitor needs to be constantly removed from the dash, there is a bigger chance of the dashboard coming apart and something breaking on the monitor. Monitors are very fragile and having one inside a car does not mean that no accidents can happen to them. Scratches are made all of the time from people getting into their car and hitting their purse against it or something similar. There are monitors that fold away when not in use and these are great for limiting scratches. They come back out when the car is turned on usually.
In conclusion, the costs of these rear cameras can be quite high no matter how they are installed. Getting them factory installed will always be the biggest cost for them. Installing aftermarket ones might have problems if they are not installed by a professional who knows what they are doing.