The Sinclair Black Watch

Turns out that the C5 was not Clive Sinclair's only failure: http://www.nvg.ntnu.no/sinclair/other/blackwatch.htm

A wristwatch that could be damaged from static electricity from a nylon shirt or carpets...

with a battery life of just 10 days...

Supplied in kit form, which was impossible to assemble... "Practical Wireless advised readers to use two wooden clothes pegs, two drawing pins and a piece of insulated wire to work the batteries into position."