Insurers such as Aetna (NYSE:AET), Cigna (NYSE:CI), and UnitedHealth Group (NYSE:UNH) usually aren't mentioned in the same breath as tech titans like Apple (NASDAQ:AAPL) and Samsung (OTC:SSNLF). However, that could soon change as insurers rely more on mobile fitness apps to save money and help patients live healthier lives.

The number of smartphone users in America is projected to rise from 164 million this year to 220 million by 2018, according to research firm eMarketer. Research firm Research2Guidance estimates that the global market for mobile fitness apps will grow to $26 billion by 2017 -- representing 61% compound annual growth from 2013. Meanwhile, rising readmissions in U.S. hospitals have forced the Hospital Readmissions Reduction Program, part of the Affordable Care Act, to raise its penalty for excess readmissions from 1% to 2% in 2014.

When we consider those three facts, it makes plenty of sense for insurers to launch mobile apps to connect to their customers.

Aetna's CarePass
Aetna's CarePass, released last year, is an ambitious attempt to unify data from various fitness apps, wearable devices, and personal health records, or PHRs, into a single app. In that sense, it's similar to the iOS 8 Health app that Apple recently unveiled at its 2014 Worldwide Developers Conference.

Popular fitness products from Jawbone, Fitbit, Withings, MapMyFitness, BodyMedia, and Aetna itself are all compatible with CarePass. Users simply need to authorize CarePass to access the app to add the information to CarePass' main dashboard. CarePass can set up a personalized fitness profile based on that accumulated information, allowing users to set up personal goals, for example: fitting into a new pair of jeans.

CarePass. Source: iTunes.

Aetna notably designed CarePass to reach the widest audience possible, by launching it on both iOS and Android and opening it to non-Aetna members. That's because CarePass is also a promotional tool that highlights Aetna's strengths over its competitors with a built-in health plan comparison app. It also helps users retain personal health data if they switch plans.

Cigna and Samsung's Coach
Cigna has taken a more conservative approach to personal health by partnering with Samsung. In May, the two companies launched their first joint product, a Samsung S Health app feature called Coach by Cigna. Since Samsung only controls 28% of the U.S. smartphone market (compared to Apple's 41%), the app will reach a much smaller audience than Aetna's CarePass.

Coach by Cigna works best when paired with one of Samsung's Galaxy Gear smartwatches, but health data can also be entered manually into the smartphone. Coach then uses that information to create a customized fitness program for its users, which then encourages them with motivational and informational messages regarding exercise routines, weight management, sleep patterns, stress management, and nutrition.

Samsung's S Health. Source: Samsung.

Coach's system "gamifies" the entire experience through achievable missions with an overall "lifestyle score" that unlocks achievement badges. Unlike Aetna or Apple's "app-unifying apps," Coach by Cigna only integrates with a handful of other apps and does not connect to PHRs or medical professionals. 

Cigna also offers a spartan members-only app for iOS and Android, myCigna, which tracks accounts, claims, ID cards, and drug costs.

UnitedHealth Group's Health4Me and texting services
UnitedHealth Group offers the Health4Me app for iOS and Android. Health4Me is restricted to UnitedHealth members who register for mobile services online. The app gives users quick access to health information of family members, as well as enabling them to find physicians nearby or speak directly with an experienced nurse for medical questions.

In terms of personal health management, UnitedHealth is taking a different approach via text messages. In mid-May, the company started offering two new text messaging services, Txt4Health and Text4Kids, to members enrolled in its Medicaid plans in three counties in Pennsylvania. The services, developed by Voxiva, send out personalized health text messages based on the user's stored health profile, such as text reminders to take medication, exercise, eat healthy foods, and attend doctor's appointments.

The Foolish takeaway
It's easy to see why insurers are releasing more mobile apps these days -- smartphone use is soaring, fitness apps are more popular than ever, and costly hospital readmissions are rising. Promoting better health habits benefits both patients and insurers, which will need to make fewer payments to cover preventable hospital visits.

The landscape for these mobile apps might change soon -- especially since Apple's Health app could become the central hub for fitness apps that Aetna's CarePass wants to be -- but they are still noteworthy ways to keep patients healthy and constantly connected to their insurers.