This helpful hint appeared 85 years ago in the British Practical Wireless magazine, November 1940. At first, I thought the idea had been sent in by Rube Goldberg, but it was actually one J. F. H. Aspinwall of Wirrall. who sometimes plugged in the soldering iron and forgot about it. His solution solved that problem, and also let him know when the iron was hot enough. He rested a piece of solder between one buzzer contact, with the other end on the iron, perched precariously above the other contact. When the iron was hot enough, the end of solder melted and the piece dropped onto the other contact, completing the circuit and sounding the buzzer.