TEMPEST attacks don't even require access to power lines, transient electromagnetic emanations leak through the air. Displays can be reconstructed from significant distance, even through multiple walls, even with no connection to the power grid. The simple fact of the matter is that once you are physically located you are totally fucked if you have a competent attacker, unless you are inside of a shielded room or using shielded equipment. All of the encryption in the world isn't going to save you, your plaintexts will be pulled from the signals that your monitor leaks, what you type will be determined from the noise of your keystrokes. Local police don't even know what TEMPEST is, DEA may or may not, FBI counterintelligence have used this sort of attack against spies though so they certainly know about TEMPEST and have the equipment required to carry out such attacks. They can monitor individual key strokes if they can get audio intelligence of typing, considering laser microphones can get audio from (something like) a mile away if they can target vibrating glass windows, I think 50 feet is a major underestimate of how far keystrokes potentially leak. Especially if they have the laser microphone hovering up in the sky on a mini UAV. Or maybe they have a dozen laser microphones on a mini UAV all targeting different windows as it goes from neighborhood to neighborhood hoping to catch something interesting . don't underestimate spies and spy catchers. Then again I have not heard of this sort of attack being carried out by police other than FBI in cases of counter espionage and counter terrorism, so it isn't standard operating procedure yet.