You can always assume permanent surveillance. Electromagnetic radiation can be read from a distance so any device is completely visible.

You’re obviously not a radio guy. Attenuation and interference are real. Many devices are adequately shielded from all but the most determined and skilled eavesdroppers. And not all equipment leaks useful information in its emissions.

If you’re really paranoid, you can build yourself a small Faraday room. It’s not that difficult. It’s also sometimes possible to buy used telco equipment sheds that come pre-shielded, they are popular with radio nerds.