Apparently on some TPMS systems the ECU has to be told if a sensor has been changed and the new one has to coded in before it will communicate. The are only expected to last 2 to 5 years and will no doubt be a target for thieves as they have a resale value
http://www.national.co.uk/tpms-sensor-valve-service-and-replacement.aspxand they are not cheap
they will be tested come MOT time and any sensor not working is a fail.
according to article
The EU estimates that the under-inflation of tyres is globally responsible each year for:
20 million litres of unnecessary fuel consumed
2 million tonnes of CO2 emissions
200 million prematurely worn tyres
9% of accidents involving fatalities
41% of accidents involving injury
always worries me when the EU estimates stuff, and those figures are global, not just in EU countries - you would expect people in EU to be more aware of tyre pressures and not need this kit