MMC (@MMC_Milad, @MMC_Jake, and @MMC_Derrick) is working on an open source sip and puff switch intended to be a cost-effective alternative to some of the commercial options. (We’ve started an editable list here of commercial and existing DIY options: Sip and Puff AT Options)
Files will be released on GitHub here: https://github.com/makersmakingchange/sip-puff-switch-analog
The current design is a battery powered digital pressure sensor enclosed in a 3d printed case. It has LEDs for visual feedback and two 3.5 mm jacks for output. The pressure thresholds are adjustable and there is a switch for controlling the power.
We’ll continue to post more details as they are available in this thread. If you have any input or may be interested in testing the device, let us know.