Service tire pressure monitor system?

If you check the tires and the pressures are all good then it's likely you have a bad sensor, the battery in them are usually good for about 6-7 years of normal use. A tire shop can check to see if you have a failed sensor and some can read the battery life as well. If you have one that shut down you may want to have them all replaced just to avoid having the light come on next week for the next one.