Beeping noises on speakers from radio waves in other devices?

Factual Questions
1

What is the mechanism of action when the following occur:

  1. A speaker makes those beeping noises when someone puts a phone by the receiver.
  2. I put my cell phone on the metal toilet paper dispenser in the bathroom and a similar pattern/ton is created

Cellphone noise on computer speakers - YouTube - this is the sound it makes

If some big metal toilet dispenser is creating these noises, then it seems - qualitatively - like it’s giving off quite a signal!

2

Well, I think it can be a few watts, more than enough to raise a ruckus.

3

I got a few good responses here.

Something I figured out later–if I want the sounds to stop (I use my Rhapsody-enabled phone in my car’s speakers), I put the phone in Airplane mode. Granted, I’m not one to answer the phone while driving, so it’s not a big deal to me.

4

  1. It’s actually surprisingly easy to make a radio receiver. All you need is a bit of metal to act as the receiving antenna, something that conducts better in one direction than the other, and a filter. That describes just about every electronic circuit ever made. In fact, engineers spend an awful lot of time trying to make sure their circuits don’t act like unintentional radio receivers (except of course when they are actually designing a radio receiver). Any time you have an amplifier in the circuit it makes things even worse, since only a tiny amount of radio noise has to get into the signal path to be amplified and be noticeable. This is why computer speakers are especially susceptible to this sort of thing, especially less expensive speakers since shielding and less sensitive circuitry costs more money.

  2. It’s possible that your toilet paper holder is acting like a radio receiver. The metal bits will act as the antenna, there’s probably a small contact area where two pieces of metal are touching that may be essentially forming a point contact diode, and the physical size of the metal bits affects the frequencies they can vibrate at, forming the filter. Voila, an instant radio receiver. It’s no more complicated than the fox hole radios soldiers would make in World War II using bits of wire and a razor blade (for the diode).

I also have to wonder if the sound is being generated by the toilet paper dispenser or the phone itself. The phone’s speaker circuit has the same general problem as computer speakers and can sometimes pick up radio noise generated by the phone’s transmitter. The sounds might be quiet enough that you don’t notice, but in the cavity of the dispenser you might be effectively making a resonant sound box that makes the quiet chirps much more noticeable.

Hold the phone close to your ear and have someone call you. If you can hear chirps coming from it before it rings, then it’s the phone itself making the sound. Otherwise it’s probably the dispenser.

Cell phones are restricted to be very low in transmitted power, something like 500 mW IIRC. Even though it’s making audible noise, it’s not enough radio power to really worry about.