Describe how the tire pressure monitor system works. On my 2006 LS430 Ultra model there are no monitoring devices present in the tire valve stems. There are no monitoring devices evident to the tire guys who install the tires. If you press and hold the tire pressure monitor button under the dash, a light comes on and says pressure monitoring is initializing - you drive it around for a block or so over 19 miles/ hour and the light goes out.
Extra credit - is the spare tire also monitored?