If I remember right TPMS sensor batteries (which are part of the sensor) last about 5-7 years. After that they fail to report and the computer turns on the light on the instrument panel.
On the older 4Runners like my 2013 there isn't a display to tell which sensor is bad. So after finding out new sensors and programming aren't exactly cheap; I just ignore the light and check my tires occasionally. Newer 4Runners have a readout of each wheel, so you can tell which one is the culprit - although they will all fail in time; so I would change all 4 if I wanted it to work again for another 5-7 years.
Also on my SR5 there is no sensor on the spare because it has a steel rim and a sensor won't fit. I think the spare is more important because you can't see it easily and Toyota installs them with the valve stem up - so they are a pain to check. So, to me, the TPMS system is more trouble than it's worth!