PDA Navigation: if you already use a Personal Digital Assistant (PDA), you can also use it as a mobile navigator. You need to connect a GPS receiver wirelessly or with a cable with your PDA. It is flexible and still offers all functions of the PDA. However, the handling can be difficult and distracting for first-time PDA users, and the voice commands can be very quiet. Car Radio Navigation: if you have a DIN slot, then you can put in stereos with an integrated navigation system. This simple addition does not need any extra units on the dashboard, but it often only supports arrow-images. Portable Navigation: these are also called "Stand Alone Systems", and they have everything they need integrated: battery, display and GPS antenna to find your way. On the road you can simply charge them in the cigarette lighter slot. Normally, they are easy to use and do not need an external antenna. Their only function is navigation and it can be difficult to fix it onto the dashboard or windshield. Cell-Phone Navigation: some cell phones can be equiped with navigation software. It is slower than other systems, and you will need a GPS receiver, too. The system is relatively cheap, and you already have your cell phone on you all the time. However, you will need an external antenna, the display is very small and the voice command is quiet. Screen Navigation: a built-in unit with a big display is top of the class among navigation systems. Furthermore, it often has additional functions like playing DVDs or receiving TV. The advantages are clear with many functions, the easy-read screen and high-comfort. The relatively high price and the additional built-in costs are the disadvantages.