These machines have two buttons on the back, a larger one and a smaller one.
After pressing the big button, the machine will enter "armed mode". The ARM LED will turn on steady, and the HEAT LED will also turn on steady.
After 10-15 minutes, when the machine is finally ready, the HEAT LED will start flashing, and we'll be able to press the small back button to fire the fog (the whole firing process lasts around 120").
More info about the device's hardware and wiring: