Hearing aids can be sold over-the-counter starting this week. Here’s how to pick one.

A new federal rule will make it easier for people with mild to moderate hearing loss to buy hearing aids over the counter, without a prescription or custom fitting.

The new rule from the U.S. Food and Drug Administration goes into effect Monday, and experts have called it a game changer that is expected to make the devices more affordable and accessible for millions of people.

With a variety of brands, styles and features to choose from, picking the right one may be daunting. Here’s some expert advice for buying a hearing aid that works for you.

Who are over-the-counter hearing aids for?

Over-the-counter hearing aids are only for adults with mild to moderate hearing loss. To ensure safety, the FDA rule has limited the peak sound output of over-the-counter hearing aids.

A good rule of thumb is that if you have the technical expertise to figure out an update to your phone’s software settings, then you are tech savvy enough to manage a self-fitting hearing aid, according to Nicholas Reed, an audiologist and assistant professor in epidemiology at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

How do I know if my hearing aid fits correctly?

Putting on a hearing aid and ensuring that it fits correctly can be tricky, especially for first-time wearers, according to Elizabeth Convery, a former National Acoustic Laboratories researcher who studied self-fitting hearing aids. In general, if a hearing aid falls out when you perform a routine action such as bending over to pick something up, it probably is not fitted correctly.

What features should I look for?

A 30-day return policy: You’ll need to wear a hearing aid for a while to determine whether it works well for you. FDA regulations require the return policy to be printed on the outside of the box.

Customization: A good hearing aid will allow users to adjust wires, tubes and tips to fit small, medium and large ears.

Different tip options: The “tip” is the part of the hearing aid that goes inside your ear. An open dome tip can create a more natural sound. Closed domes boost sound. Power domes are good for those with greater hearing loss.

Ear wax filters: Make sure the part of the hearing aid that goes into your ear comes with a filter to prevent ear wax buildup. A filter will help the device last longer.

Custom volume adjustment: Look for hearing aids that self-adjust the volume at different frequencies, said Blake Cadwell, a hearing aid user and the founder of Soundly, a website that compares hearing aids. If a product doesn’t do this, “you might as well not be wearing a hearing aid, because you’re amplifying all the wrong sounds,” he said.

Directional microphones: Some hearing aids can detect noisy environments and adjust the direction of the microphone to compensate. How well that feature works depends on a manufacturer’s algorithms and the sophistication of the microphone, said Brian Fligor, an audiologist and the owner of Tobias & Battite Hearing Wellness in Boston.

Background noise filter: If you’re having trouble understanding others when you are in restaurants, parties or other noisy environments, a hearing aid with a filter to dampen background noise can help.

Bluetooth connectivity: If you own a smartphone, Fligor recommends looking for a hearing aid that offers Bluetooth connectivity, which can help for activities such as speaking on the phone, listening to music and streaming a movie.

Warranties: Most prescription hearing aids have warranties of at least one year, and many have three year warranties, according to Heidi Hill, an audiologist with the Hearing Health Clinic in Minnesota.

To learn more about the hearing aid options available, users can search free online comparison tools such as HearingTracker.com and Soundly.com.

Where can I get an over-the-counter hearing aid?

Eventually, hearing aids will be widely available at retail pharmacies and chain stores. Some retailers are moving faster than others to take advantage of the new OTC rule. In some cases retailers may first offer hearing aids for sale online and then begin selling them in stores in the coming days or weeks.

Best Buy announced that it plans to open hearing centers in over 300 stores this month, where staffers with specialized training can help customers choose among devices from nine over-the-counter brands ranging in price from $200 to $3000.

Walmart plans to offer over-the-counter hearing aids online and at its vision centers, and prices will start at $199.

Walgreens also plans to offer Lexie Lumen hearing aids for around $800 in stores and online nationwide.

How much should I expect to pay?

Experts expect the price of over-the-counter devices to go down but said a quality product can still be expensive. Retailers have announced over-the-counter hearing aids ranging from $199 to $3,000.

If you’re considering an over-the-counter hearing aid with a price point of $1,000 or more, experts advise comparison shopping with prescription hearing aids. You may find a prescription aid with better features and higher sound output, with the added benefit of a custom fitting with an audiologist.

How long does it take to adjust to a hearing aid?

Because hearing involves both the ear and the brain, your brain needs time to adjust and relearn how to process sound, said Barbara Kelley, the executive director of the Hearing Loss Association of America. “You don’t just put in a hearing aid and poof, you just magically hear the way you’ve always heard before,” she said.

Adjusting to new hearing aids can be more difficult for people whose hearing loss has gone untreated for a long time, Hill said. A new hearing aid may feel annoying at first, but it should never be uncomfortable to the point of being painful.

The fastest way to get used to a new hearing aid is to wear it all the time, even when you’re alone. To start, try to wear them for at least six hours a day.

For the first two days, avoid noisy and chaotic environments. Then, ease yourself into a variety of settings. To help you adjust, listen to music or an audiobook, or try apps with listening exercises such as BrainHQ or Amptify.

How do I take care of the hearing aid?

Moisture is any electronic device’s worst enemy. Wipe off your hearing aids every night with a dry microfiber cloth to remove any dirt or dust. You can also use hearing aid sweat bands to protect the devices when you’re working out. Drying devices for hearing aids also are available. Change the wax guards on your hearing aids about every three months to help the devices last longer.

When should I seek medical advice?

Anyone can consult an audiologist for a professional hearing test, even if opting to purchase a hearing aid from a retail store.

A sudden hearing loss, especially if it’s only in one ear, is considered a medical emergency, said Sarah A. Sydlowski, an audiologist with the Cleveland Clinic and president of the American Academy of Audiology. Other red flags that should prompt a medical visit include dizziness, fluid drainage from the ear, ringing in the ear or feeling pressure or pain in the ear.