Piezoelectric harvesters are considered an alternative power source for applications that can support low to medium data rate transmissions in wireless sensor networks where ambient vibrations can provide microwatts to milliwatts of power. In this paper, we report the design and performance of a proof-of-concept (POC) autonomous sensor-node prototype including: an in-house piezoelectric harvester; a power management unit (PMU) made of discrete components; and an in-house ultra-wide band impulse radio (UWB-IR) transmitter. The piezoelectric harvester provides 54 mu W at 3.3V(rms) at 450 milli-g and resonant frequency of 160 Hz. In these conditions, it was observed that the sensor node is capable of sending 1 burst of 100 pulses every 110 seconds consuming an average of 8.2 mu W, which is much less than the generated energy. The POC sensor node using kinetics energy harvester shows energy autonomy, thus opening range of possibilities for sub 100 mu W energy harvesting wireless sensor nodes.