"Take a breath," the watch told her.
A few minutes later, it pinged again. "Take a minute to breathe," it said.
The watch's health app also was tracking her heart rate, which spiked to 120 beats per minute, then 130.
The last message from the watch said, "Seek medical attention."
So Recktenwald told her mom, who was sitting with her in church on a recent Sunday.
Stacey Recktenwald, a registered nurse, monitored her daughter's heart rate for about an hour and confirmed the results from the watch. She took her daughter to an urgent care clinic, where doctors and nurses seemed skeptical.
"They didn't believe us at first," Deanna Recktenwald said. "But then they took my pulse and told us we should go to the emergency room."
Blood work taken at Tampa General Hospital revealed the teen's kidneys were barely functioning, at just 20 percent. A biopsy later would lead to the diagnosis of alport syndrome, a genetic condition characterized by kidney disease.
"Deanna is a healthy child. She had no other symptoms," Stacey Recktenwald said. "I'm just so grateful for the watch."
To her, it had been just a fitness device, with not a piece of medical equipment.
But the Apple Watch's abilities as a health monitoring system have piqued the interest of physicians worldwide, said Dr. Peter Chang, chief medical informatics officer at Tampa General.
"This technology started with the Fitbit, which tracks steps. But the Apple Watch can in fact track heart rate, and this device and others are being used by physicians to 'fill in the gap' information-wise from when a patient leaves the hospital or doctor's office, to when they see them again," Chang said.
The watch uses green LED lights on its underside to detect the amount of blood flowing through the wrist and track the heart rate. Other wearable tech devices use low electric pulses to do so.
Chang says these tracking methods are, for the most part, fairly accurate.
"Because of this technology, and Bluetooth, we can use the information saved on something like an Apple Watch and import it into our medical records systems at some hospitals," Chang said. "Some studies show that tech like this can be just as accurate as an EKG (electrocardiography) reading."
In November, the U.S. Food and Drug Administration approved the Apple Watch's heart rate monitoring system, making it the first medical device of its kind to receive FDA approval. Apple also launched an initiative called the "Apple Heart Study" where the company will collect heart rate data for future research.
Chang thinks this is just the beginning.
"There are devices that can track weight gain and other health concerns," he said. "But wearable devices like the Apple Watch provide the lowest cost way for patients to keep track of their health and manage better outcomes."
Deanna Recktenwald is on the road to recovery, which will require life-long maintenance of the syndrome and a potential transplant later in her life. But the senior at Foundation Christian Academy in Valrico is looking forward to a bright future, with plans to attend Southeastern University in the fall.
"I want to be a nurse practitioner like my mom," she said. "I do believe the watch was a blessing."
Deanna got it as a Christmas gift and uses it mostly to check Instagram, her mother said.
"If she went away to college not knowing about this condition, who knows what could have happened?"
After the trip to the hospital, Stacey Recktenwald reached out to the Silicon Valley technology company to express her thanks.
"On the Apple website, there's a box to send messages but I couldn't put my gratitude into 600 characters or less," she said. "So I called the Apple Store and they forwarded it on to corporate."
Soon after, Recktenwald got an email from Tim Cook, the CEO of Apple.
He thanked her and said he was glad Deanna was OK.
About the Author