A solution for proximity detection of an object is disclosed. According to an aspect, there is provided a portable training computer, including a communication circuitry configured to operate according to Bluetooth technology; a radio frequency radiator circuitry coupled to the communication circuitry and configured to receive transmission signals from the communication circuitry and radiate the transmission signals as transmission bursts; a measurement circuitry coupled to the radio frequency radiator circuitry and configured to measure an electric property of the radio frequency radiator circuitry and to determine proximity of an object with respect to the radio frequency radiator circuitry on the basis of the measured electric property; and a controller configured to synchronise measurement timings of the measurement circuitry with the transmission bursts.