A method includes delivering a Radio Frequency (RF)signal having a time-varying power from an intra-body probeto tissue in a vicinity of the probe in order to ablate thetissue. A temperature is measured in the vicinity of theprobe. A decision is made as to whether the probe is incontact with the tissue, by comparing the measuredtemperature to a temperature threshold that varies in timedepending on the time-varying power of the RF signal.
