Sorry to resurrect an old topic.
If automatic switching were to be attempted for a VV or VW type mod, I think that a highly chipped box implementation would be the way to go. Splitting the air intake via a specialised mouthpiece would prevent air from having to be drawn through a great distance.A sensitive differential pressure vacuum sensor connected to a microprocessor would allow advantages (customisability of response, profile of response) over a simple membrane based suction switch. A physical toggle switch could provide some security against miss-firing. Likewise safety protocols could be programmed into the electronics. I've summarised this with the attached crude drawings.
I was influenced by this instructional:
http://www.instructables.com/id/Arduino-Controlled-SIP-PUFF-Switch/?ALLSTEPS... which recommends the differential pressure switch shown at
www.designflexswitches.com/switches/psf102.php for an arguably similar project.
As well as the internal atomiser system and accessibility of internal components in the billet box mod:
http://www.billetboxvapor.com/
