Now I think about it, my Timemaster 1034 LED alarm clock (as it calls itself on the sticker underneath) may be the oldest still-working electric or electronic thing I own -- or at least, the oldest that I've had from new (the Quad hifi and the Mac Plus are second-hand). It's operated continuously for at least the last 20 years, possibly 25. Though nowadays it's only a safety-net: I find I wake up most days half-an-hour before it goes off anyway.

Peter