This work presents the development of two low cost RF energy harvesters dedicated to the ISM bands. The rectifiers exhibit respectively a maximum of power efficiency of 47% and 33% at 900MHz and 2.4GHz. Focusing on the sensitivity, the harvesters provide a 1V output voltage at 3m with a radiated power of 27dBm at 2.4GHz, and 11m with a radiated power of 30dBm at 900MHz. The demonstration of energy scavenging is further proposed by the remote powering of a clock (0.9V/5uA) during the download of a video with a cellphone in GSM mode, and then the data broadcasting in bluetooth mode by a tablet.