Hearing aids and mobile phones haven’t always gotten along as well as they do today. The complex electronics in both products often triggered static, dropped words or squealing interference noises. Technology enhancements along with new government regulations have largely eliminated this problem. Nowadays cell phone – hearing aid compatibility is not the challenge it once was. To help consumers shop for the right hearing aid compatible mobile 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). In M mode, the hearing aid uses the internal microphone to detect sounds and amplify them. When the hearing aid is in T mode, instead of the microphone it uses its built-in telecoil to directly pick up conversations from inside the phone, in the form of electromagnetic signals. Roughly 60 percent of all cell phones sold in the United States have a telecoil (T) mode.

The two modes – M and T – are each rated on a scale of 1 to 4 where 1 is the lowest sensitivity and 4 is the highest. No mobile phone or cordless handset sold in the United States can be sold as hearing aid compatible (HAC) unless it has a rating of at least M3 or T3.

Hearing aids and cochlear implants have a similar M and T rating system to certify how sensitive they are in each mode, and how resistant they are to radio frequency interference. If you know the M and T ratings for your hearing aid, to determine its compatibility with any mobile phone, just add the two sets of ratings together. If you get a combined total of 6 or more, that is thought of as excellent, a combination of hearing aid and phone that will be highly usable. A sum of 5 is considered normal and should work fine for typical mobile phone users. A combined rating of 4 is considered usable for brief calls, but may not be suitable for extended phone use.

If you are shopping for a mobile phone online, you can usually use this combined rating to determine how compatible the phone you are interested in buying 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.