Tire pressure monitor systems have a battery that can wear out after 5 years or so. Solution? Replace the battery for fifty cents or whatever a battery costs? Nooooo, of course not, one has to replace the entire sensor, $90 parts/labor per sensor, one in each tire. 
It is useful to have the sensor, long before air pressure becomes a problem (flat on the freeway) one knows that there is a problem. But I wish I could just replace the battery.

It is useful to have the sensor, long before air pressure becomes a problem (flat on the freeway) one knows that there is a problem. But I wish I could just replace the battery.