At some high-end hotels, new computer systems that connect individual rooms to network servers can now keep track of guests’ preferences and change the room conditions automatically. These “smart” systems can learn whether a frequent guest likes the lights dimmed, the curtains closed or the room toasty. They can also personalize the electronics so that John Coltrane, for instance, greets jazz buffs when they enter their rooms. And sensors in refrigerators alert maids when the minibar is running low on soda.