The FCC thinks in terms of legal priorities and international treaties for keeping RF neighbors playing nice, and especially protecting public safety and emergency services. As such, it classifies devices within a regulatory plan. A device may have traits covered by that plan, and others not so. One cannot presume anything about a device’s unregulated characteristics from regulatory limits on other narrow criteria.
Part 15 sets limits for intentional radiators, and unintentional radiators. That would include baby monitors, garage door openers, RF alarm sensors, and Wifi networks as intentional. Most receivers, digital devices, etc. that aren’t intended to transmit but incidentally can are unintentional radiators. In general intentional radiators are restricted to bands of frequencies that may cause problems to similar devices, but not to protected services on other frequencies. Unintentional radiators are presumed to potentially cause problems from 9 KHZ to light, and be restricted to signal leakage levels less likely to do so.
Nearly anything can act as an antenna, including a grounded case, to receive or transmit.
Under the wrong circumstances, there can be conflicts between devices with combinations of signals that normally wouldn’t cause serious problems. Under extreme conditions (eg, making a PC and phones work at a high power transmitter site), it can take serious work to get non-RF devices, never mind receivers, to work properly or at all. Enough RF can rectify and power lights with no AC connection, never mind do odd things to semiconductors.
If a non-priority device of any kind (including licensed transmitters) causes harmful interference (as legally defined), the FCC can generally order it shut down. That’s at times included cable premium channels leaking from defective coax near aviation frequencies. It includes some light bulbs. (Yes, the FCC can come into your home or business and order you to turn off and replace lights.) That includes 250 watt paging transmitters interacting with 50 KW broadcast transmitters, if they’re harming aviation.
Part 15 devices are at the bottom of the pecking order. They’re often cheap items, though not necessarily. They can be $6000 industrial test gear or $100,000 instruments. They can be 37 cent production cost toys. They can be the receiver section of a transceiver, the other half of which is licensed. You’re free to buy whatever quality you prefer or need, but if what you buy doesn’t meet your needs relative to protected causes of RF interference, a Part 15 device has no “rights” (claim for legal protections against other devices or their users), while other devices may or may not have “rights” against Part 15 devices. The $6,000 Part 15 device is just as unprotected as the 37 cent one.
Usually cost is what drives lower quality and more susceptibility to malfunction under adverse conditions, such that consumers pay for just what they get. No matter the cost, there’s no such thing as an impervious design. In the case of a protected service being harmed, the Part 15 device always loses. In the case of various Part 15 devices, everyone loses if users don’t negotiate resolutions, though it’s their problem and not one where anyone has a legal claim.
Again, you’re free to buy whatever quality you prefer and can afford. Part 15 isn’t about that, but defining standards for what can be made to transmit in unlicensed use, and background noise levels that determine when devices are harmful, without which assault lawyers could duke it out for those who could afford to pay.
Part 15 would limit what neighbors with crappier electronics than yours could do to harm your ability to receive emergency signals (mostly by manufacturer controlled limits the user doesn’t change). It doesn’t say how good your electronics need to be otherwise. That’s your problem.