Every carpenter's dream: a Morse code handsaw.
It was made of an ordinary handsaw like this.
The handle was first removed...
... and then attached to this position. Now the handle is free to rotate a bit and the upper screw acts as a switch when it touches the blade.
Keying cable was connected under the screws. The other end goes to a CW transmitter or an audio oscillator.
This is how it works: