Cheap, ubiquitous, and brilliant, esp. the beep on the hour function. After over ten years of all kinds of conditions on a sea kayaking buoyancy aid, beep used for keeping track of tides, now redeployed at desk keeping track of time in the day whilst working from home. Need to make sure you turn that beeping off before bedtime though...

Haven't worn one on a wrist for over fifteen years, and don't intend to restart. Macro(ish) effect courtesy of an LED magnifying lamp.