[onceiwasthere]

I've wondered the same thing. The only thing I can think of is some kind of god awful false positive rate. Which doesn't really make sense either considering the technology we have today.

[moralestapia]

Right? To add,

These guys have been doing exactly that for decades, and with very simple sensors and microcontrollers,

https://www.youtube.com/watch?v=IngelKjmecg