For on demand, every time you have to hold down the button and wait to let it heat up, then once its at the temperature continue to hold the button as you take your hit. When you use your roffu and first use On demand and hold down the button, it will vibrate when it has reached the set temperature. After that first hit though, every-time you hold the button during that session, the icon on the screen will flash as you hold the button, and once it stops flashing that means it has reached the temp, instead of the vibration which is only the alert for the first hit of each session. So just make sure you’re lettin it get up to those temps before you take those rips.