Love Alarm is an app that tells you if someone within a 10-meter radius has a crush on you. It quickly becomes a social phenomenon. While everyone talks about it and uses it to test their love and popularity, Jojo is one of the few people who have yet to download the app. However, she soon faces a love triangle situation between Sun-oh whom she starts to have feelings for, and Hye-young, who has had a huge crush on her.
The app Love Alarm is created to notify users when someone within 10 meters likes them, without revealing who it is. Kim Jo Jo, a high school student who lost her parents at a young age, lives with her aunt's family, which makes her life difficult. She doesn't download the app because her phone is too old.
Hwang Sun Oh, a popular student from a wealthy but emotionally distant family, attends the same school as Kim Jo Jo. His best friend, Lee Hye Yeong, likes Kim Jo Jo, and Hwang Sun Oh kisses her to confirm his feelings.