If they're detecting it based on electric fields they absolutely won't be able to pull off usable range outside of an area with absolutely no big collection of metal (can not be used near buildings or roads)

Typical range for sensors that can pick up human electric fields (mostly generated by muscles and nerves) is a few meters. If you try to boost it enough for long range outdoors use then your sensor is gonna get screamed to death by the sun and atmospheric noise

The signal to noise ratio problem is analogous to trying to pick out a specific voice in a crowded stadium. It's too loud to be able to pick up one source.

So the desert is like that, where there's a lot of background electrical noise that's louder than the electrical signals that a human heartbeat makes.