Argentieri works for P3, a company that performs radio-frequency interference hunting for nationwide carriers including Verizon, AT, T-Mobile, and Sprint.

The device he’s waving around is a portable spectrum analyzer, a machine that helps him home in on sources of interference.

This is a delicate process that involves knocking on strangers’ doors, searching their homes for the offending device, and politely reminding the owner that they could be fined up to US $16,000 a day for keeping the gadget switched on.

In the United States, popular LTE bands include 700 megahertz, 1900 MHz, and 2.5 GHz.

Both carriers and regulators take this restriction seriously—electronics manufacturers must have their gadgets certified by the FCC before selling them in the United States.

But some rogue devices inevitably slip through.

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