According to a recent report, shipments of Zigbee modules are set to increase by more than 700 percent over the next five years. Zigbee, for anyone who is unfamiliar with the brand, is a wireless technology that allows us to incorporate physical objects like light switches or water valves into intelligent networks. Though Zigbee is only one of several options available, the concept is being applied to increase efficiency and save energy everywhere from factories to living rooms. As we add more and more "things" to this globally connected network, we also have more and more radio waves swirling about in the air around us. Understandably, this has prompted questions from both the public and the media about whether wireless technology poses a health risk to humans. The discussion normally begins with cellular phones, but consumers may be left wondering about other wireless products as well. Notably, the World Health Organization, the US FDA, and numerous organizations around the globe have repeatedly confirmed that there is no credible cause for health concerns when it comes to the ubiquitous cellular phone. They say that the devices simply aren't capable of negatively affecting the human body at the power levels at which they operate. Whether you remain skeptical shouldn't really matter, as we're going to explain why low power wireless products are entirely different.
When regulatory bodies such as the FCC evaluate the safety of wireless devices, they do so by assigning each device a Specific Absorbtion Rate (SAR). A device's SAR rating is a concise expression of how much radio frequency energy (or heat) is absorbed by the body when the device is used as directed. The key elements in gauging potential impact to to the human body are power level, duration of exposure, and proximity. A typical mobile phone has a transmission power rating of about 500mW, though maximum output may vary depending on network and environmental conditions. By comparison, Zigbee and the home networking-specific Z-Wave each transmit at around 1mW. All things being equal, this represents a reduced potential impact to the tune of about 500 percent. (To be sure, at extremely high levels, radio transmissions or radiation do have the potential to compromise human health. Essentially, this is due to excessive heating of tissue and the body's inability to cope.) An SAR rating is only required for wireless devices intended for use within 20cm of the body. Few Zigbee or Z-Wave products, especially those built for home control, fall within this parameter. What this means for consumers is added piece of mind. Even with cellular phones, the SAR drops off dramatically when the device is moved just a few centimetres away from the body. What's more, devices that incorporate Zigbee or Z-Wave radios spend most of their time in sleep mode, only transmitting data at distant intervals when not in use. Z-Wave nodes, for instance, have a duty cycle of about 1 percent, meaning that 99 percent of the time, they're not sending out any radio frequency energy at all. Oversight agencies like the FCC also take duty cycle into account when calculating SAR. For example, let's say that a device has an output power of 100mW, but only transmits 10 percent of the time. At that point, SAR is more accurately calculated using an adjusted output power of just 10mW.
So, the basic idea that we're trying to communicate here is that even if you remain unconvinced by all of the reputable studies that say cellular phones are completely harmless, there's no reason to lump all wireless devices into the same category. Technologies like Zigbee and Z-Wave show extraordinary potential, making everyday life more comfortable and energy efficient while helping to modernize industry and the energy grid. All the while, they operate at a fraction of the power of handheld phones, from relatively distant points, and at incredibly infrequent intervals.