In the past, the sophisticated electronics of cell phones often interacted badly with the electronics of hearing aids, causing interference between the two devices that was perceived as static, squealing or whistling noises, or lost words. Thankfully, advances in technology and new government regulations have made the question “Will this phone work 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.

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, 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. Roughly 60 percent of all mobile 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. 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.

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 sum of 6 or more makes a solid pairing. That hearing aid and mobile phone combination should work well for you. If the combined rating is 5, this combination is considered normal and suitable for most regular phone use. 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.