The aim for this thesis was to investigate if harvesting of ambient radio waves could be a viable source of energy and where and when it can be used. A survey of the signal strengths at different locations in Uppsala, Sweden was performed which showed that the cellular frequency bands were the ones that carried the most energy. One circuit was manufactured and two more were simulated, together with the circuitry required to measure and display how much energy that was being harvested. The design was tested at the same locations as the survey of the signal strength was conducted at. The maximum harvested energy was 35µW which was at a location inside in a window facing a cellular transmittor with an approximate distance of 100m. At 200m away from a cellular transmitter, the output was 1µW. In a typical city environment, the output from the harvester was 0µW. The harvesting technique was also compared to energy from solar- and thermal energy. The comparison showed that it is almost always more beneficial to use an alternative source of energy, such as solar cells, even indoors.