[throwup238]

> or if you are lucky authentic ones that for some reason ended up there (but I can't imagine a way).

Chinese fabs are notorious for running secret shifts that make their customers’ chips to sell themselves. They’re the exact same chip but made without authorization, using the customer’s exact design.

That said, Sensirion has their own CMOS fabs in Switzerland so that’s very unlikely to be the case here. If they work at all, the counterfeit chips are probably some Chinese CO2 sensor IC that's small enough to fit into the same package, lightly customized to fit the pinout of the original. Or it's just a microcontroller inside faking it a la FTDI.

[tobi1449]

Huh, good points. It doesn't seem to be just a micro sensor faking it, as it reacts as expected for example when opening the windows. I guess the only way to tell if they are any good is to buy a verified good CO2 sensor and compare the outputs then.