Combine with an Arduino Leonardo or DFRobot Beetle and a Big Red Button.
Beetle available at DFRobot. Button at Okaphone (Netherlands) or Rapid (UK).
Wiring is quite simple, I don't have a diagram for it but it goes as follows for the DFRobot Beetle: one connection of the button goes to A0 and the other connection goes to GND (- on the silkscreen of the PCB). THAT'S IT!
The code is a bit convoluted, this is becasuse I avoided using a library for the button debounce. Large buttons like these tend to be quite "noisy", so they absolutely need debounce.
Since I wanted my customers to be able to modify the code themselves as easily as possible I chose to implement the logic without libraries. This still requires the Arduino IDE. Nowadays I might have used CircuitPython to achieve this without even needing to install software.