Medical alert systems: In vogue, and for some, invaluable

My elderly dad is sporting a cool new mobile device these days, complete with a sleek design and an aluminum cover. It's not a smartphone or a laptop or a tablet; it's a medical alert system, a one-button gadget that can summon emergency help. "Many older people who live alone embrace the devices, because they worry how they would get help if they fell and couldn't get to a phone. And it's reassuring for their kids to know there's a backup system in place," says geriatrician Dr. Suzanne Salamon, assistant professor at Harvard Medical School.

The devices weren't always so popular. Once the target of comedians (an issue that kept some seniors from using them), medical alert systems are now in big demand, perhaps due to an aging population, advances in technology, and the reality that one in three adults ages 65 and older might fall one day. Throw in a higher comfort level with mobile gadgets, and it's not a big surprise that sales of the systems are rising steadily, expected to reach $21.6 billion by 2020, according to some marketing research estimates.

Lots of choices

The popularity of alert systems has resulted in a flood of choices. There are dozens of brands, and each company has several systems available.

Basic models

These typically consist of a pendant or wristband with a large electronic button, and a base unit (similar to a speaker phone) that you plug into your house phone jack. If you get into trouble, you simply press your button, which signals the base unit to call the alert system operators. The operators then talk to you through the speaker in the base unit, and send paramedics if you need help. Most gadgets are waterproof, and have built-in batteries that don't need recharging; most batteries last for years, and will be replaced free of charge if they run out. Just like a wireless house phone, these buttons can signal the base unit only within a limited range, such as 400 feet. But the buttons don't provide two-way communication with operators; only the base unit does that.

Typical price: $25-30/month.

Mid-grade

This type of model usually come with a base unit and a wearable button, and they also upgrade the technology to include fall detection, an innovation that automatically contacts emergency operators if it detects a fall (handy if you're unable to push your button).

Original versions of automatic fall detection weren't the most reliable at discerning if you'd fallen or just leaned over. Newer versions claim to have worked out the kinks, promising much higher accuracy, as much as 95%.

Typical price: $30-40/month

Premium models

These products upgrade the button to top-of-the-line devices that use cellular technology to contact emergency help. The improved communication allows you to use the alert system wherever you go, whether it's the grocery store or the great outdoors. Unlike the other options, this device has a built-in speaker, so you can talk to an operator through the button. It also features global positioning system technology (GPS), which gives alert system operators the ability to send help to your exact location. This button is thicker and larger than the type worn only at home, so you probably won't be able to wear it comfortably on your wrist—you'll have to put it in your pocket or wear it around your neck. Also, it must be charged every few days, just like a cell phone. If you're not faithful about that, the button won't work. Typical price: $40-50/month

The fine print

It's not enough to find the latest and greatest alert system. Make sure that the company you choose has no long-term contracts, low activation fees, no cancellation fees, discounts for add-ons to your service, free replacement for equipment that's not working, and most important: operators available 24 hours a day. Many alert system companies meet those standards, so it may help to get a recommendation from a friend, your doctor, or even a local hospital.

And remember: no matter what kind of device or deal you get, the alert system will be useless if you don't wear it. "Not everyone remembers to wear the device, or they're stubborn about them, or they take them off to take a shower, which is a place people often fall," says Dr. Salamon.

In my dad's case, the medical alert system is always around his neck. He has a premium model that looks a lot like a mini-cellphone. But believe me, the peace of mind the device brings to all of us is absolutely super-sized.