Hi Idaho,
When you take a draw on your e-cig, the air pressure on some
batteries causes a wheel switch to activate. A membrane in the battery causes the switch to spring back and turn off once you stop inhaling.
In newer automatic
batteries, there is a microphone type switch built into the battery that detects the sound and vibration when you draw on your e-cig and activates the atomizer.
Hope that helps.
Sun