I guess this is just a looser interpretation of “airtight” than what I’ve previously experienced in life. In my experience, “airtight” means “zero exchange of air in or out”, but this setup is a controlled process where the only place air exchange occurs is through the heat exchanger. However, from these descriptions, it’s not the same sort of “airtight” as what I’m accustomed to. Not trying to say that anyone is incorrect, just that it’s different from what’s familiar to me and that’s why I was confused.
Sleep as Android has a CAPTCHA mode that prevents you from shutting off the alarm without some form of verification, like solving a math problem or scanning an NFC tag or bar code.
I struggle mightily with mornings and have been late to work countless times because I can unconsciously shut off my alarm. But with the CAPTCHA mode I can’t shut the alarm off without physically getting out of bed, carrying my phone into the other room, and scanning an NFC tag. It’s been a life saver.
I haven’t seen such a feature in any other alarm app.