Until the late 1990s, the RAF's nuclear bombs could be activated using a bicycle lock key.
(The BBC's Newsnight discovered that until the early days of the Blair government the RAF's nuclear bombs were armed by turning a bicycle lock key. Allegedly there was no other security on the bomb itself. Just imagine James Bond, no tamper-proof combination locks which could only be released if the correct code was transmitted, just get a bike lock key James. Not very exciting is it?)