First of all you have to install 4 3mm LEDs inside the button and the three holes.
After some cleanup the button should slide smooth throught the hole.
Then you have to install a small pushbutton underneath the button and fix it inplace inside of the thermaldetonator.
After wireing everything up you need to glue some magnets on to the inside edge(you could also glue the two halfs permanently in place if you don´t need anymore acess).
I powered the whole thing with a 9V blockbattery and used a cheap china arduino nano clone.