The method according to the invention is intended to be applied in a situation where the power level of the signals transmitted by that mobile network to which the terminal is connected sink below predetermined threshold levels. Then the terminal is arranged to measure the power levels of signals transmitted by the base stations of at least one second system. The method according to the invention comprises advantageously steps in which the cellular radio system at first transmits to the terminal at least one threshold value. Then the terminal measures the strength of the signal transmitted by at least one base station and compares the measured signal strength with said threshold value. If the signal strength of the received signal is lower than said threshold value the transmission mode is changed to a mode where the measurement of the signals of a second system can be performed. A terminal according to the invention comprises advantageously means with which the steps of the method presented above can be performed.