I tried the cheaper TYRE GUARD which were not very accurate and alarmed regularly with false readings. Ie I had to stop and check for an alarmed deflated tire, only to find all was OK.Very annoying!and unreliable. The old Peter and the wolf syndrome! I now have run Truck Systems Technologies from the USA, and self proclaimed leaders in the tire monitoring market. This tyre (tire) monitoring system appears to be no 1 in blogs etc. The new 507 allows either the button style cap sensors for rubber valve stems, or flow – through sensors for metal valve stems. In-tire sensors are also available. They require factory replacement of batteries every 5-7 years, which requires breaking the bead to expose the sensor inside the tire! For full details see.... http://www.tsttruck.com/ The accuracy is 1-2 PSI and has the capability of monitoring a B double semi trailer. I have a booster mounted in the rear of my LC 200, just to be doubly sure of good reception. I have only done 2,000kms with the van on, and about 20,000kms of highway, around town, and some off-roading, without any issues with the "button" style sensors. My set-up is 6 sensors on the LC 200 (two spare tires on the rear) and 6 sensors on the Kedron ATV including the spares. I possibly would not bother monitoring the spares, and save 4 monitors. TST were very helpful when purchasing my requirements. Trust this may help you with your selection of a tire monitoring system.