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Maker uses Raspberry Pi and AI to block noisy neighbor's music by hacking nearby Bluetooth speakers
(www.tomshardware.com)
This is a most excellent place for technology news and articles.
I don't know where you're from, but the vast majority of cars in the US have hollow doors. The only exceptions might be expensive luxury cars. There is no foam in them. If you poured milk in them it would most likely drain out of small holes in the bottom, although it might splash & stick to some of the internal components and make a smell.