Wireless technologies such as mobile telephones, wi-fi and Bluetooth, bring enormous benefits and convenience. And, with the exception of accidents caused by inattention, there have been no cases of any harm arising from use of this technology. Yet doubts remain. Since the communications frequencies used are known to be hazardous at high power many have asked whether the technology is absolutely safe at the low power levels used in practice. This talk looks at the issues involved from first principles, and the relevance of the Specific Energy Absorption Rate (SAR) is discussed and demonstrated.