Wearable wireless Internet of Things (IoT) devices are targeted for the next generation of smart digital consumer electronic solutions. It is desired that future devices do not require regular changing or charging to operate, however most IoT power sources are either disposable or based around rechargeable batteries. As energy harvesting technologies emerge as a potential and attractive solution to this issue this paper presents an experimental survey of the best current commercial energy harvesting solutions, determining how realistic energy harvesting technology is for current and future wearable devices. It explores empirical results for thermoelectric harvesting (using body heat), RF harvesting (at 915 MHz), and photovoltaic techniques in the context of body-centric wireless nodes. These have several advantages when compared to other forms of energy harvesting (such as mechanical-based harvesters) as they require minimal maintenance and have no moving parts which offers long lasting reliability and noise free operation. The results indicate a significant issue for realising the next generation of wearable wireless solutions and thus reviews the future advances in this area to understand how bleak the horizon really looks for body-centric battery-less wireless solutions.