On Knock Sensors, I wouldn't trust anyone to MFG them but a real electronics manufacturer. And frankly I find it more plausible that VTT just looked through a parts catalog and found something based on a few specs they came up with.
And for the stock ones and 'false knock'.
Has anyone played with bolt TQ? Bolt material? Adding a fiber/plastic washer to the top side (between sensor and bolt head)?
Also, I highly doubt anyone can actually "hear" knock. Or have any way to correlate it to a position or cylinder.
You may hear a resonate frequency, but the actual impact, not a chance. The Doppler Effect plays a part here.
Now if you're running that sound through a sound card and looking at the waveform, then you might have something.
Some guy with a pair of headphones on, LOL. Nope.