New home and business phones sold in the US have been Hearing Aid Compatible since the 1980's. That's nice, but nobody really knows what Hearing aid Compatible means!

There are two ways for modern hearing aids to pick up sounds:

1. Through an internal microphone.

2. Through a T-Coil (Telephone Coil) that hears sounds by magnetism.

Hearing Aid Compatible in relation to phones simply means that the receiver in the handset not only plays the audio of the conversation like a speaker in a radio (into your ear), but it has a magnetic signal  that you can't hear as well.

The magnetic signal can be picked up with a coil of wire attached to an amplifier that turns the magnetic signal into an electrical signal, that can be sent to a hearing aid or even a tape recorder. There used to be a little suction cup thing that you would stick on a handset and then plug into a tape recorder to record a conversation, which used magnetic induction just like a T-Coil.

The T-Coil in a hearing aid is a loop of wire that picks up the magnetic signal (through induction). The real benefit is that the hearing aid wearer turns off the microphone in the hearing aid while they're using the T-Coil, which eliminates the annoying squeal every hearing aid without a T-Coil makes - that the hearing aid wearer often can't hear.

The squeal is simply feedback, like you'd hear if you stood too close to a public address speaker while holding a microphone. When the user of a hearing aid without a T-Coil turns up the hearing aid's volume, the microphone in the hearing aid can hear the speaker in the hearing aid that much louder, so feedback occurs.

When the user of a hearing aid with a T-Coil flips the switch from M (for Microphone) to T (for T-Coil), the microphone in the hearing aid is turned off entirely, and the only "sounds" the hearing aid can hear are the magnetic signals coming from the receiver in the handset. Because the microphone is shut off, feedback can't normally occur (unless there's feedback between the telephone's handset microphone, and the hearing aid).

These are the controlling facts of Hearing Aid Compatibility:

1. If the hearing aid doesn't have a T-Coil, it won't work properly with a telephone handset that's Hearing Aid Compatible. 

2. If the telephone handset receiver doesn't put out enough of a magnetic signal, it's not Hearing Aid Compatible, and it won't work correctly with a hearing aid with a T-Coil.

The history of Hearing Aid Compatibility is interesting. For many years, all of the phones rented out by Bell Telephone Companies were hearing aid compatible. The way the receiver element in the handset was made, it put out a large magnetic signal that hearing aid manufacturers took advantage of to eliminate the feedback or squeal.

After the Carterphone decision in 1968 which allowed you to connect your own phones to Bell phone lines, Japan started selling phones in the US that were cheaper than Bell phones. Some of the receivers in the Japanese handsets didn't have the magnetic signal, which was taken for granted by that time in the US, so hearing aids didn't work with those Japanese phones.

In the late 1970's, the FCC made a rule that all phones being sold in the US had to have Hearing Aid Compatible receivers in their handsets by the early 1980's. The Japanese phone manufacturers simply added a coil to the receivers that didn't already meet the US specs, and everything was back to where it was when all of the phones were Bell phones - as far as hearing aids we concerned.

In the early 1990's the FCC made a rule that said that all of the Japanese phones that were in-use at businesses, that were sold before the Hearing Aid Compatibility rule, had to be retrofitted to make them Hearing Aid Compatible. That meant either replacing the receiver element in the handset, or replacing the whole handset if it was sealed and the element couldn't be replaced. Amazingly enough, the FCC changed their mind the day before the rule was supposed to take effect in 1993, and said "never mind." They said if a company had an employee with a hearing aid, the company had to make sure their phone was Hearing Aid Compatible (which made a lot more sense).

In the early 2000's, the FCC made a rule that all of the phones sold in the US should be "amplified." That meant that there had to be a volume button or wheel to turn up the volume in the handset. In addition, if the volume could be set so it was very loud, the phone was supposed to return to normal volume when it was hung-up, so the next person using the phone didn't have their hearing damaged. None of this makes a difference whether the handset is Hearing Aid Compatible.

If a telephone's handset does contain a Hearing Aid Compatible receiver, and the phone or handset has an amplifier, the magnetic signal from the receiver will be stronger than from a non-amplified handset - but the T-Coil in the hearing aid is supposed to be made to pick up the magnetic signal of an unamplified handset. An amplified handset isn't necessary to use the T-Coil in a hearing aid.

Even though all phones have been Hearing Aid Compatible since the 1980's, hardly anybody knows what Hearing Aid Compatibility really means...

Hearing Aid Compatibility simply means that the receiver in the handset puts out a magnetic signal, in addition to the audio signal.

The confusing part is that the hearing aid  has to be made with the T-Coil to be able to work with a Hearing Aid Compatible phone. If it doesn't have a T-Coil, the hearing aid can only use the built-in microphone that's also used for normal conversations, and it will almost assuredly squeal.

Many of the companies selling hearing aids don't educate their customers - their goal is just to shake as much money out of them as possible. If their customer doesn't understand how to use their hearing aid, or its capabilities, the customer is definitely not making an informed purchase and there's going to be bad blood down the road. Sometimes the hearing aid dealer blames the hearing aid's limitations on the phone, which usually isn't the case.

If the hearing aid has a T-Coil, it will have a little switch that the user can move to choose between the microphone and T-Coil. With the constant miniaturization of hearing aids, it's become difficult to put a switch on a device that small, that a user can flip. The next innovation in hearing aids was the automatic T-Coil switch.

It turns out that most receivers in handsets put out a permanent magnetic field, in addition to the magnetic signal that's picked up by the T-Coil. Most handset receivers are a basically a tiny dynamic speaker, with a permanent magnet and a cone (diaphragm).

Hearing aid manufacturers decided to make use of that permanent magnetic field to turn on the T-Coil automatically when the hearing aid was near the handset receiver. When the wearer holds the handset to their ear that the hearing aid is in, a little magnetic reed switch in the hearing aid is activated by the permanent magnetic field, and the T-Coil is switched on automatically (switching off the microphone at the same time).

That's a nice idea, except  that there is no standard for how strong the permanent magnetic field is in the handset. It could be none, it could be a little, or it could be a lot. The strength of the permanent magnetic field has no relation to either the audio coming out of the handset receiver, or the magnetic signal that the T-Coil couples to. It's just how the receiver manufacturer decided to design their receiver - and it's likely that when it was designed nobody gave any thought to someone using the permanent magnetic field to turn on the T-Coil in a hearing aid.

Hearing aid manufacturers picked some arbitrary amount of magnetism that's necessary to activate the tiny reed relay in the hearing aid. That means the hearing aid may or may not activate the T-Coil when the handset is held up to a particular in-the-ear hearing aid. If it doesn't, there' probably no manual switch for the wearer to move, so the hearing aid wearer just can't use use a phone who's handset doesn't put out enough of a permanent magnetic field.

In the past almost all handsets looked the same. In the last few years, almost every handset looks different - often a really strange shape. A lot of those handsets are sealed so they can't be taken apart. There are no screws, or the screws are in addition to solvent or sonic welds that can't be broken without destroying the handset. If the handset can't be opened it's difficult to replace the receiver in a handset with one that puts out a stronger permanent magnetic field, because the handset can't be opened. In many cases, another type of handset with a receiver with a stronger magnetic field won't fit on the phone itself.

The bottom line is that if a hearing aid wearer has an automatic T-Coil switch, and the wearer is trying to use a phone without enough of a permanent magnetic field to turn on the automatic T-Coil switch, the wearer won't be able to use the phone with the T-Coil even though the handset is Hearing aid Compatible.

The symptom of the automatic T-Coil switch not working with a particular phone is squeal. If the wearer is sure the hearing aid has a T-Coil, and it has an automatic switch, if there is a squeal when the handset is held to the ear with the hearing aid, the microphone is still live - so there is squeal.

The fix is to get a handset with a receiver with a stronger permanent magnetic field. That's either done by putting a different type of handset with the same electrical characteristics - but a stronger permanent magnetic field (like from a different manufacturer) on the phone, or replacing the receiver element in the existing handset with one with a stronger permanent magnetic field.

Since it's possible that a handset simply has a defective receiver element, the quickest test is just to swap handsets with the handset on one of more other phones to see if they work. If they don't work, the hearing aid wearer is either going to have to get a hearing aid with a manual T-Coil switch, change the handset or receiver on the phone, or use an entirely different brand of phone.

In some cases, it may be possible to epoxy a small powerful magnet near the receiver of a handset to activate the automatic T-Coil switch. These tiny powerful magnets are often called "rare earth magnets."  If the handset can be opened, it may be possible to hot glue the magnet inside, near the receiver.

My personal opinion is that a problem with an automatic T-Coil switch is not a shortcoming of the phone, but of the design of the hearing aid.

While this applies to corded or cordless home or business phones, it doesn't apply to cell phones. In general, each cellular provider should have a couple of models of phones that are Hearing Aid Compatible, but they aren't required to make all of the models Hearing Aid Compatible. If the phone you like doesn't work with your hearing aid, you don't have any recourse other than to use a different phone that does work.

Keep in mind that while a couple of models of cell phones are supposed to be Hearing Aid Compatible, that doesn't mean those phones with work with an automatic T-Coil switch. There are no FCC rules that say anything about an automatic T-Coil switch, so you may need a hearing aid with a manual T/M switch to be able to use a particular model phone.