Tornadoes can move very rapidly and with amazing power so people need to have time to take shelter. The technology we have in place today allows for most tornadoes to be tracked. The weather channels will have information available when the conditions are right for tornadoes to possibly form. This way people can make sure they are prepared as much as possible.
A tornado watch means that there is a strong possibility of a tornado forming in the area. A tornado warning means that an actual tornado has been sighted out there and people need to be aware of where it is located. Your local weather channels will interrupt program as well as run information along the bottom of the screen to let you know about tornado watches and warnings. There is usually a radar screen shown that has a color coding system for the various areas that are being affected.
Sometimes tornadoes form very rapidly though and there isnt time to get warnings out over the TV. When they are developing at night and people are sleeping they arent going to get them. In such instances a very loud siren will be sounded and that is an immediate notification to take shelter. Dont take the time to turn on...