Your phone habits could signal a stressful day, new KAIST study finds

Your smartphone may be able to tell you when you are having a stressful day based on how you use it, a KAIST research team has found.

The AI-assisted technique, developed by a team at the KAIST School of Computing, assesses users' daily stress based on the everyday tasks they repeatedly perform on their phones, the university said Thursday.

The best-performing model identified stressful days with an average accuracy of 75.9 percent among participants tracked for about a month, and 73.8 percent among those tracked for about 105 days.

The research ties mental health monitoring to the smartphone, a device most people now carry everywhere. Because phone usage records capture changes in everyday behavior over time, they are increasingly used as a digital indicator of mental health conditions such as stress and depression.

Earlier studies mostly measured screen time or which apps people used, but those numbers can change whenever someone switches apps. The researchers gave the example of someone who moves from KakaoTalk to WhatsApp or Line. The app changes, but the task stays the same: chatting on a messenger.

The KAIST team instead focused on what users do on their phones rather than which apps they use, so the data stays consistent even when people switch apps.

The team analyzed data from 26 university students and office workers in their 20s and 30s, divided into 16 short-term participants, who participated for 30.5 days on average, and 10 long-term participants, who took part in the study for 105.1 days on average. The participants provided both phone data and daily self-assessments on stress, which were used to create a personal model.

The best-performing model distinguished stressful days from stress-free ones with an average accuracy of 75.9 percent for the short-term group and 73.8 percent for the long-term group.

The study showed a link between phone habit and stress, not that any habit causes it. The research also did not record what users typed or what their messages said, to protect privacy. Instead, it logged how often a person typed and how they moved between screens.

"We looked at the smartphone not simply as a device that measures usage time, but as a living space where a person's communication, information searches and financial activities repeat," said Prof. Lee Ui-chan of KAIST's School of Computing.

“By turning complex smartphone records into units of behavior that people can understand, this study lays the groundwork for analyzing long-term changes in mental health more reliably,” Lee said.

BY CHO YONG-JUN [[email protected]]