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I was sitting next to my grandpa (Tato), who wears a hearing aid, on the couch. I’ve noticed that when the landline telephone rings I actually hear the phone ring through his hearing aid (less than one second) before I actually hear the landline ring. At first, I thought that I was imagining it but it has now happened several times. Can someone explain how something like this is even plausible?

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    $\begingroup$ Many hearing aids link to devices like phones and TVs through e.g. Bluetooth... $\endgroup$ – user10851 Jul 23 '14 at 3:47
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    $\begingroup$ so the question is "what type of hearing aid?" maybe as Chris says it is designed to catch phone signals which, as they come, must radiate electromagnetic waves too. $\endgroup$ – anna v Jul 23 '14 at 4:26
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    $\begingroup$ @ChrisWhite: his hearing aid does not link to any device. That was my first assumption, which turned out to be incorrect. I should of put this detail in my question to be more clear - sorry. $\endgroup$ – Carlos Jul 23 '14 at 6:21
  • $\begingroup$ Pretty cool technology, eh? Your grandfather must be involved in the trials of the new temporal-predictive hearing aids. They're built with limited prescience regarding things like the telephone ringing, the microwave beeping, the doorbell being pushed, etc, because it takes older folks a bit longer to get to things. By the time these are available on the open market the plan is to have them "lead" reality by up to ten seconds. But keep quiet about this until the SEC can figure out how to regulate this vis-a-vis the stock market. Thanks. $\endgroup$ – Bob Jarvis - Reinstate Monica Oct 17 '14 at 17:33
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I will amplify my comment:

Hearing aids operate in one of two modes, acoustic coupling or telecoil coupling. Hearing aids operating in acoustic coupling mode receive and amplify all sounds surrounding the user; both desired sounds, such as a telephone’s audio signal, as well as unwanted ambient noise. Hearing aids operating in telecoil coupling mode avoid unwanted ambient noise by turning off the microphone and receiving only signals from magnetic fields generated by telecoil-compatible telephones. In the United States, about 60 percent of hearing aids contain telecoils, which generally are used by individuals with profound hearing loss.

A telecoil is a small, tightly-wrapped piece of wire inside the hearing aid that, when activated, picks up the voice signal from the electromagnetic field that leaks from compatible telephones. While the microphone on a hearing aid picks up all sounds, the telecoil will only pick up an electromagnetic signal from the telephone. Thus, users of telecoil equipped hearing aids are able to communicate effectively over the telephone without feedback and without the amplification of unwanted background noise. Telecoils can only fit in two styles of hearing aids: “In The-Ear” and “Behind-The-Ear” aids. Most smaller hearing aids are not large enough to fit the telecoil

So, check your grandfather's hearing aid if it has a telecoil.

The delay is natural between two different signal processing telephones. My wireles rings on the second ring of the main line phone .

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Most telephone handsets will not start ringing the instant a ring signal is received through the telephone line. Possibly this is to avoid them ringing due to random bursts of noise on the line, though I would guess this isn't much of a problem with modern digital lines. I use a SOHO phone system and I can see the system status signalling a call a second or two before my handset rings.

Exactly why your Grandpa's hearing aid is picking up the ring signal I can't be sure. However the ring signal is an oscillating voltage of about 100V at a frequency of 20Hz, and telephone lines are quite good aerials. I'd guess the hearing aid is picking up the EM waves generated by the ringing signal.

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Caller ID is sent after the first ring. Ironically, even though phone companies sequenced things that way to avoid delaying the first ring, some phones want to avoid bothering people until after the caller ID information is received or would be expected (if the caller hangs up or someone answers the phone before the caller ID information is sent, there might be no indication of who called).

I'm not sure what exact conditions would cause the ring signal to be detected by a hearing aid, but since many hearing aids are designed to be receptive to small signals when there aren't any larger ones around, the 20Hz signal might not have to be very strong in order to be noticeable.

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