Tyre Pressure Monitoring System (TPMS). Having experienced a flat tyre a year or so ago whilst traveling on a French motorway which I only noticed when we pulled into an aire for fuel I decided that I would invest in a TPMS on our current van. Expensive (about £100) but easy to fit and set up – the model I bought was solar powered so just sits on a convenient spot on top of the dashboard. I was surprised how the tyre pressures and temperatures vary whilst on the move.