in the US it has become a regulation that manufacturers should be able to notjust monitor but maintain the tire pressure. the pump is in the center hub cap and is powered by the wheel's rotation.
Thanks for the link. sana lahat ng oto meron ganyan iwas sa hassle eh. Minsan malalaman mo na lang na flat tire mo pag pansin mo dipping to one side ...or worse for those with low profile tires in cars di mo pansin yun..