Pyroelectric cells based on fabricated screen-printed PZT and commercial PVDF films are proposed as thermal energy harvesting sources in order to supply low-power autonomous sensors. The cells are electrically modelled as a current source in parallel with output impedance. Heating and cooling temperature fluctuations generated by air currents were applied to the pyroelectric converters. The generated currents and charges were respectively in the order of 10−7 A and 10−5 C for temperature fluctuations from 300K to 360K in a time period of the order of 100 s, which agrees with the theoretical model. Parallel association of cells increased the generated current. The dependence of the generated current on relevant technological parameters has been also characterized. Finally, current from cyclic temperature fluctuations was rectified and stored in a 1 F load capacitor. Energies up to 0.5 mJ have been achieved, enough to power typical autonomous sensor nodes during a measurement and transmission cycle.