Hearing aids and cellular phones haven’t always gotten along as well as they do now. The sophisticated electronics in both products often caused static, lost words or squealing interference noises. Fortunately, advances in technology and new government regulations have made the issue “Will this phone work together with my hearing aid?” simpler to answer. The regulations mandated new labeling requirements and ratings that help you to find a cell phone that works well with your hearing aid.

The first thing you need to understand is that hearing aids operate in two different modes – microphone or “M” mode, and telecoil or “T” mode. In M mode, your hearing aid uses its built-in microphone to pick up audible sounds from the environment and amplify them so that you can hear them. In T mode, the hearing aid uses telecoil technology instead. The hearing aid is able to pick up the electromagnetic signals from inside the phone directly. 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 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. To be sold in the United States as hearing aid compatible (HAC), a mobile phone or cordless handset must have 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. When shopping for a phone, to determine its compatibility with your hearing aid, simply add its M and T ratings together with those of the phone to create a combined rating. 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.

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.