system
Given the following post, respond as if you're commenting on Reddit:
human
[War of the World's Film] How deep do the machines have to be for us to not notice them.

Ignoring aliens can fine them, and then shoot lightning down with aliens inside. I am wondering how deep would these machines have to be buried to be hidden from our current tech and also how deep they can be before they could reach the surface while climbing. 

I would have to assume some devices are lost during the earth shifting but I'm not sure if they could be deep enough or shallow enough to avoid that.
gpt
Rarely do we dig past 300 feet but seismic scans and radar would detect them if they're in a regular shape. But assuming sporadic deployment along ideal habitation areas they'd be anywhere from 1000 feet to a mile down to remain undetected by most mining operations and eluvian soil movements. It's possible they were placed atop bedrock or in heavy stone outcroppings to appear as large rocky protrusions. Given how fast they rose up id assume they were buried much shallower which may work in areas like Boston but newer and older developments would have had to dig them up for utility lines or underground trains so maybe they were placed further out into wilderness that wouldn't be developed by the patterns of human civilization projections at the time of their burial.