A tire pressure monitor and a method of measuring a pressure in a tire include a decision whether the tire pressure should be measured. The decision is made in dependence on a magnitude of a change in a signal which is output by a sensor which senses the pressure prevailing in the tire or the temperature prevailing in the tire. As a result it is possible to reduce the size and the weight of the components of a tire pressure monitor to be accommodated in the tire or in the rim to a minimum.