Today we're talking about a vehicle's TPMS, or tire pressure monitoring system. A TPMS is what tells your car when it's time to turn on the low pressure indicator light.
On many vehicles, the low-pressure light is all you get. You don't know which tire it is or how low it is. On more complex systems it will actually tell you left-front or right-rear. On the most complex systems it will tell you in real time the exact pressure of each tire.
How does this system work? There's actually a transmitter inside the tire, right here behind the valve stem. A module like this is attached to the back of the valve stem. Before they put the tire on, they insert this through the rim and then lock it on. This module transmits the tire pressure information to the vehicle's computer.
If you get in your car and you see the light, get out, walk around and check all your tires. If you don't have an obvious flat you've probably got a slow leak, and more than likely, you're okay to drive it to a repair shop and have it checked out. If this light comes on while you're driving you need to pull over immediately. Again, it could be slow leak or it could be a sign that you're about to have a blowout.
These things do have batteries inside, and they can't be changed. They're supposed to last about seven years or a 100,000 miles. So don't be surprised when you go to buy new tires and the technician tells you, you need new TPMS sensors.