I missed one bit... The circuit leaks current even when off so that the 3.3V rail stays active at about 0.7V. I think it's via the charge status line from the charging circuit. It's not a huge current, but it will affect the lithium cell's standby time, especially in storage. Especially as the low voltage rail has the sensor's heater across it. Thankfully the resistance of the heater seems very high.
Maybe that's why they used the alcohol sensor, since the real sensors may have a much lower heater resistance.

I find fake stuff like this hilarious. It makes me think that someone who actually believes this is monitoring carbon dioxide is going to get emotional when they've had some wine and the CO2 level goes off the scale.

The self latching power button circuit is very neat. It's the electronic equivalent of a standard motor starter with latching contactor contact.

The most useful bit of this video is the science of tin oxide sensors. What I showed is little more than a crude oversight to quite a complex scientific subject. The exact composition of the metal oxide layer is what determines the gasses detected, and there are usually other vapours and gases that will be detected alongside the desired one. But the payoff is the simplicity and ruggedness of the sensor. As you can see in the video, the resistance change is dramatic for even a whiff of gas or vapour.

Further examination of the display does show that it's a fixed use monochromatic display with coloured panels printed over the circular segments. That's a shame, as it would otherwise have been an excellent base for a custom display unit.

The use of a random cheap sensor to give the illusion of being real by genuinely reacting to environmental changes is amusing. I've a horrible feeling they may also pull this stunt on detectors that actually matter, like gas leak or carbon monoxide detectors.


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