Hearing aids and cellular phones haven’t always gotten along as well as they do today. The intricate electronics in both devices often triggered static, lost words or screeching interference noises. New government regulations, together with considerable improvements in both phone and hearing aid technology, have made this incompatibility uncommon. To help consumers shop for the right hearing aid compatible cell phone, the new regulations include a standard rating system and labeling requirement.
Understanding the rating system requires a bit of knowledge about the modes that hearing aids can operate in. There is an M mode (which stands for microphone) and a T mode (which stands for telecoil). When your hearing aid is in M mode, it uses the built-in microphone to pick up audible sounds from around you and amplify them to make them easier for you to hear. In T mode, the hearing aid instead uses an inductive process to pick up electromagnetic signals inside the phone directly, without the need for a microphone. The T mode is important when shopping for a phone, because at least 60% of hearing aids sold in the U.S. have one.
The rating system for these two modes of hearing aid operation uses a scale that ranges from the lowest sensitivity (1) to the highest sensitivity (4). To be labeled as hearing aid compatible (HAC) a cell phone must carry a minimum rating of M3 or T3.
In addition, many hearing aids (and cochlear implants) have a similar M and T rating to measure their sensitivity and their resistance to radio frequency interference. To determine the compatibility between your hearing aid and a mobile phone you are considering, just add the M and T ratings together; add the M rating of the hearing aid to the M rating of the phone and add the T rating of the hearing aid to the T rating of the phone. A combined rating of 6 or more is considered excellent, a hearing aid/phone combination that would provide highly usable, interference-free performance. A sum of 5 is considered normal and should work fine for typical cell phone users. If the combined rating is 4, this is thought of as acceptable but not very usable if you make a lot of extended phone calls.
This combined rating system makes it easy to shop for a mobile phone online, because it easily allows you to determine how compatible it will be with your hearing aid. In the end, nothing beats a real world test so you may want to wear your hearing aid to the mobile phone shop and test out a few different phone in real conditions.