Quantity   Component name
1 × Telegraph key An old Soviet telegraph key that I bought from https://www.ebay.co.uk/str/dentalodessa (not affiliated or sponsored). Any momentary switch will technically work though.
1 × Pimoroni Tiny 2040 I used this because it's small enough to fit into the telegraph key's base, but it's wildly overpowered for this simple application so you can use something else if you prefer.
1 × Passive piezeo buzzer You can skip this if you don't want it to make a noise.
1 × USB C cable You can skip this if you don't want the device to work.