Wearable technologies (‘wearables’) describe electronic devices which can be worn on, or implanted in, the body. Wearables encompass a wide range of technologies, from pedometers which count steps to research-stage ‘smart tattoos’ which could monitor cardiac rhythm. Twenty years ago, wearables were commonly basic LCD-screened pedometers. Today, even mid-range wearables often estimate heart rate and rhythm. Options for wearables go beyond the wrist, such as the Oura ring, and the nascent emergence of a smart clothing market. Measurements which wearables record also go beyond external measurements; continuous glucose monitors are commercially available today. Wearables undertake over 35 types of measurement [1], and advanced sensors in development promise more.There has been a sharp increase in the interest, sales and sophistication of wearables over this millennium, from the …