Sleep monitoring is a boom industry, mirroring what devices and apps such as Fitbits and Strava have done for physical activity. Market reports vary on the value of this industry, but it is clearly lucrative and growing rapidly. A quick search reveals a wide range of devices – rings, headbands, watches and other wrist-worn devices, under-mattress devices and bedside devices – all suggesting their use will unlock such quality sleep as to make Rip Van Winkle jealous.