Courtney Cheng’s smartphone reminds her when it’s time to meditate.

Cheng, 25, a nonprofit project manager in the San Francisco Bay Area, is a paying member of Headspace, one of a handful of apps focused on meditation and wellness that have accrued millions of users — and millions of dollars in venture capital investments. She said she found the app after dealing with a “post-grad crisis” after college. Now, it helps her relax and fall asleep.

But like the many other smartphone notifications Cheng receives throughout the day, she isn’t always in the mood to hear from Headspace.

“I set a reminder on Headspace to send me a notification to remember to use it,” Cheng said. “But it makes me laugh because sometimes I’m like, ‘I don’t want to pick up my phone right now.’”

Smartphones have trickled into almost every part of modern existence, and meditation and wellness are no exception. Device use is so common, detox programs are now popular — and the average person receives 65 to 80 notifications a day, according to research from Duke University. The paradox that even meditation apps may be the cause of anxiety has not stopped millions from turning to devices for relief, making it a lucrative new market in the app economy.

“It does seem silly that it’s just another thing to do on my phone,” said Sarah Gordon, 25, a project coordinator at Cincinnati Children's Hospital, who pays for Headspace and uses it almost every day. “Even though I don’t touch my phone while using the app, the second I open my eyes, I notice myself go to grab my phone.”

Users like Cheng and Gordon have contributed to the growth of this new market, proving consumers are willing to pay for apps that provide some mental relief. Cheng pays “just under $100 a year” for the apps, a price she says is worth it. Calm, another popular meditation and sleep app, charges about $70 for a year.

That success has been met with sizable investments from venture capital firms. Headspace has raised $75 million from investors, while Calm recently topped that, raising $88 million and being valued at around $1 billion.

I’ve never once opened the headspace app because their notifications awaken such a pure rage from deep within — Lauren Franklin (@Franklinsays) March 8, 2019

The rise of these apps has coincided with growing concern among consumer advocates, wellness gurus and even big tech companies about smartphone addiction. Michael Acton Smith, co-founder and co-CEO of Calm, said that smartphones can still be a force for good.

“The mobile phone gets a lot of bad press, but if you use it correctly, it’s an incredibly positive thing in our lives,” Acton Smith said.

He noted that wellness apps have gained popularity due to a cultural shift away from overworking.

“A few years ago, people would show off how little sleep they had,” Acton Smith said. “Now, people are horrified by that.”

That cultural shift is something investors hope to capitalize on.

“Look at Nike. People took running, branded it, and made it a lifestyle,” Nicolas Wittenborn, a principal at Insight Venture Partners, one of the investors in Calm, said. “Yes, there was a business purpose, but it helped people become more fit and have a healthy lifestyle. We want Calm to take a similar path.”

Sleep, wellness and meditation have already shown signs of becoming fodder for new lifestyle brands. Arianna Huffington, co-founder of HuffPost, turned herself into a sleep guru, while a broader industry has grown around the idea of self-care.

I’m digging the push notifications from headspace, tbh. pic.twitter.com/nmc9TI3RMr — Luis M. (@lcm1986) February 22, 2019

Kevin Rose, an internet entrepreneur who is now a venture capitalist at True Ventures, operates meditation app Oak, which is free. Rose said that while he sees benefits in the apps, he also noted that they're a good business because they are relatively inexpensive to run.

Rose said Oak supports more than 140,000 monthly users and only costs about $700 per month to run, making it reasonably easy for him to offer it free.

“They’re phenomenal businesses if you look at the margins,” Rose said of meditation apps. “It doesn’t cost these mediation companies anything to serve this content. It’s really inexpensive to create and ... these concepts have been around forever.”

While it might not cost much to record a guided meditation, it is a bit more expensive when it's read by Hollywood actor Matthew McConaughey, like on Calm.

Rose said that paying customers can be more engaged due to the value they put on the apps but said that he has some reservations about what the business model means for users.

“I think a lot of the apps today, the way they frame it is they just have large amounts of content,” Rose said. “I worry about people thinking they need the next pack.”

“We want people to get off their phone and actually practice on their own,” Rose said.

Experts that spoke with NBC News said meditation and sleep apps can be good for people trying to manage stress, but are not without drawbacks.

I hate when software I use to improve my depression (ie meditation and fitness apps) use a streak tracker. It just makes me feel even worse about my bad days when I can’t keep up. Feels like yet one more failure. — Bearcat in the Hat (@bearcatinthehat) January 17, 2018

“There have been a lot of studies of meditation and its benefits, both for physical and mental health,” Janet Kennedy, a sleep doctor in New York City, said.

Dr. Dianne M. Augelli, an assistant professor at the Weill Cornell Medicine Center for Sleep Medicine and physician at New York Presbyterian, cautioned that sleep and wellness can be complex issues that won’t be solved by an app.

“Expectations need to be tempered about what they can do,” Augelli said.

One obvious impediment to sleep the apps pose that both Augelli and Kennedy pointed out: screen time.

Screens emit “blue light,” a type of wavelength that suppresses melatonin, one of our main hormones for sleep.

“Some of the apps are just audio, which is fine, but we don't recommend any that flash or that have you look at an orb to do your breathing work,” Augelli said.

Kennedy also worries the apps are making their users overthink sleep.

“There is a downside to all of the attention sleep is getting,” she said. Most of the apps offer streaks and track how much you use them. Some record how much you end up sleeping.

Kennedy thinks sleep shouldn’t be something you set a goal for, like training a marathon. “It’s a different process. Your body is going to do what it’s going to do.”

Ultimately, Augelli says that if the apps are helping people wind down before bed, that’s a good thing. “Some people will read, some people will listen to something on an app that is soothing.”

“Not too long ago people had CDs or tapes to help them fall asleep.” Now, Augelli said, they use apps.