For the past month I’ve been testing this device as a way to maximize my fuel efficiency. Keeping your tires inflated is critical to good gas mileage. I over-inflate because I don’t need great traction. I get decent traction already due to the short wheel base my car - a Scion iQ.
Inner rim valve stem monitors can only alert you if the tire is changing pressure constantly (meaning you are 5psi or more off spec)
The valve cap style measures actual psi to the ½ psi measurement.
The best price can be found on eBay for about $50 shipped.
Retail and Amazon is $80 + shipping.
My research indicates that this particular setup, four tire stem caps and a car 12V cigarette plug called “Carchet” is the best setup with the most reliable readings.
These have a special tool (that comes in the package) required to take them off.
You also must have the reader/display - as these won’t work with any other system - for added security.