Computers were once big RF emitters, but the FCC cracked down on that successfully in the 1980s. In the early days of personal computing, a Radio Shack TRS-80 and a Milton Bradley Big Trak would both crash if close. In recent years, most computers got radio receivers for at least WiFi, and thus had to be built well enough not to knock out their own receivers.
Analog TV sets tended to emit loudly at the local oscillator frequency. The UK used to drive around with "television detector" vans to find people who didn't pay their TV tax, which funds the BBC. But tuners quieted down years ago, as they became tiny RF-tight sealed units.
The worst behavior comes from switching power supplies, especially for lighting. The cost pressure is very high. They don't receive, so they have no receiver to protect. Another big source of noise is leaky cable TV systems. Again, since they don't receive, they aren't affected by their own leakage. The cable industry has successfully lobbied to escape tight restrictions on cable system leakage. Those two sources are probably the source of most problems.
Low-cost spectrum analyzers are available, and some are laptop peripherals.[1] There are ones as cheap as $69 on eBay, but the consensus in EDN is that you have to pay a few hundred dollars to get something that produces useful measurements. People who install and maintain WiFi networks in large buildings usually have one. Then you can find what's blithering all over the spectrum.
[1] http://www.edn.com/design/test-and-measurement/4412405/Low-c...
CRTs used to emit the picture on their screen well enough you could receive it over a nontrivial distance. This is called Van Eck phreaking.
https://en.wikipedia.org/wiki/Van_Eck_phreaking
OTOH, being able to receive a signal and being able to nail down where it's coming from and who's broadcasting it are two very different things, and the location part is substantially harder. Using the Van Eck technique, or any other, to crack down on people not paying the BBC license fee would have cost more than the fee was worth. Psychological ploys with faked-up vans, however, are a lot cheaper, and can be fairly effective.
Um, yeah, about that, that would be really nice if it were true. Maybe sometimes for some hardware in some situations. For a 1st gen motorola droid X I can personally guarantee when the wifi gets unusually frisky the bluetooth drops out. Very annoying when listening to music on a BT earpiece. A hardwired headphone never drops out, but a main marketing point of USB-C is to get rid of headphone jacks because they work well and they're too cheap to profit off.
The cable leakage thing was true in the 80s, but the FCC wisely put pretty low transmit level limits on all the two-way gear (settop boxes, cablemodems, cable phone modems). To make a long story short if signals are getting out, interference is getting in and is measurable and is likely causing an upload/upstream problem. If you think microwatts of output power from a cracked cable is annoying to a fm radio listener, imagine a "miles long" cable with a crack acting like an antenna across the street from a 50 kilowatt am transmitter and consider its effect on modem upstream speeds. Problems will happen, but it'll get fixed pretty fast, unlike the 80s or something. Maybe a decade ago the journalists made a sport of complaining about digital phone service being unable to dial 911 and that was the end of unrepaired cable leakage problems.
Oh so that is why my bluetooth audio gets choppy when I walk past the wifi access point in the hallway? I've never even thought about that before other than been annoyed by it.
How utterly inconvenient that they occupy the exact same frequencies. I should probably get a 5 GHz wifi access point...
God help you if you wanted to listen to am radio or watch broadcast TV when you had a c64 powered on nearby.
I just can not imagine how it can put much power in any frequency other than the <150 kHz ones, that aren't really that valuable.
My guess (and it is only a guess) is that the problem is mostly from unregulated imported electronics that emit all kinds of broadband RF noise as a consequence of being made cheaply.
So no, proliferation of cell phones is only a problem for cell phones (one of the reasons for migrations 2G -> 3G -> 4G). The real problem are other devices transmitting in cell phone spectra effectively DDoS'ing them.
Look toward a city skyline at night. Or even a small town. You'll see a blended haze of light reaching up into the sky. Probably a similar deal with the general radio spectrum emissions, now that everyone's carrying the equivalent of pocket RF flash lights, and walking in proximity to the RF street lamps that cell phone towers have become.