The movie begins by showing how a sophisticated mobile application called Love Alarm works,
which can detect the whereabouts of the secret admirers within ten meters.
The app will notify if the secret admirers are close but don't specify the person.
Love Alarm is loved by high school girls who wish to live a happy romance.
However, this is not the case with a high school girl named Kim Jo-jo, a beautiful and
hardworking high school student who is bright and cheerful, despite her family's painful
history.
Living a difficult life and working hard to make ends meet, Jo-jo has no interest in Love
Alarm, never even downloading it.
Every day, Jo-jo works as a waitress at a diner.
Even though her life is hard because she has to work hard, however, she works with passion
and never complains about the life she has to live.
On the other hand, a young man named Lee Hye-yeong, who also works at the diner, pays attention
to Jo-jo and keeps an eye on her secretly.
Hye-yeong has a childhood friend, a young man named Hwang Sun-oh, who recently returned
from overseas.
Sun-oh then tries to call Hye-yeong, but he doesn't pick up the phone.
He finds out that Hye-yeong works at a diner and then leaves to meet his childhood friend.
When he got there, Sun-oh saw Hye-yeong secretly following Jo-jo after work.
Hye-yeong seems to harbor feelings of love for Jo-jo but does not dare to express it,
so he just observes her from a distance.
While waiting for the bus to arrive at the bus stop, Jo-jo spends time making origami
frogs from the leaflets she found there.
She plays origami happily, making Hye-yeong, who watches her, happy too.
Not long after, the bus that Jo-jo had been waiting for finally arrived.
She gets on the bus and chooses a seat by the window to see the scenery outside.
At the same time, Jo-jo meets Sun-oh, staring at her from inside the car, and they stare
at each other.
Long story short, Sun-oh and Hye-yeong finally met and missed each other by teasing each
other because they were best friends.
Sun-oh, who is currently attending the high school where Hye-yeong attends, soon becomes
a popular student at school because of his very handsome face and cool appearance.
Because Sun-oh downloaded the Love Alarm application, he received a notification on his cellphone
indicating that many women were crazy about him.
The scene then switches and shows Jo-jo looking very sleepy.
One of her classmates approached her and told her that she had to come to the teacher's
room immediately because their homeroom teacher had called her.
She then rushed to the teacher's room.
However, just as she was about to climb the stairs, Jo-jo bumped into Sun-oh, and they
stared at each other for a long time.
After that, Jo-jo, sitting alone, was approached by her best friend, a girl named Kim Jang-go,
who told her about Sun-oh, a transfer student at their school who became very popular with
the girls because of his good looks.
Unlike Jang-go, who looks amazed by Sun-oh's handsome face, Jo-jo takes it casually.
Meanwhile, Sun-oh is standing on the sidelines, engrossed in his cell phone, so he doesn't
notice a ball rushing toward him.
Luckily, Hye-yeong saw it, got there in time, and protected him from getting hit by the
ball.
When everyone seemed amazed by the unique heart-shaped cloud phenomenon in the blue
sky, a young man named Duk-gu secretly watched Gool-mi, a beautiful girl who was also Jo-jo's
cousin.
Duk-gu seems to like Gool-mi, but she doesn't seem to have the same feelings toward him.
The next day, Jo-jo, fighting with her boyfriend, Jang Il-sik, ran away from him and hid behind
a tree.
However, Sun-oh, knowing she was there, told Il-sik, so Jo-jo became annoyed with him.
On his way home, Sun-oh sees Jo-jo sitting alone at the bus stop and looking down.
He quietly follows her when she decides to go somewhere before heading home.
However, Jo-jo immediately finds out about Sun-oh's whereabouts and asks why he is following
her.
He diverts the conversation by saying he has something to say to her.
All this time, Sun-oh seemed to think Jo-jo liked him, so he asked her to kiss him.
Suddenly she is very surprised to hear that and then refuses his request because she already
has a boyfriend.
However, Sun-oh seems to ignore that Jo-jo has dated Il-sik and then kissed her.
She stays silent when Sun-oh kisses her.
They then ran away to take shelter because it was going to rain soon.
Not long after, Jo-jo finally arrives at her workplace, a convenience store run by her
aunt, Gool-mi's mother.
Because her parents are dead, Jo-jo now lives at her aunt's house and has to work hard to
help her aunt and pay for her grandmother's medical expenses, who are being treated at
the hospital.
However, her aunt always treats Jo-jo cynically because her parents, who died, left behind
a pile of debt, and they have to pay for it.
Elsewhere, Sun-oh, the only son of a wealthy family, always feels lonely because he thinks
his mother is always angry with him and doesn't like everything he does.
While Sun-oh was brooding alone, Hye-yeong arrived and tried to comfort him.
But Sun-oh asked about Hye-yeong's feelings for Jo-jo, where he always denied his feelings
for her.
Sun-oh then tells Hye-yeong that he kissed Jo-jo.
Suddenly Hye-yeong was very surprised to hear Sun-oh's confession and chose to leave him.
On the other hand, Jo-jo can't get Sun-oh out of her mind after he kisses her.
However, she then feels guilty about her boyfriend because she let Sun-oh kiss her.
After discovering that Gool-mi actually likes Sun-oh, Jo-jo tries to avoid him as much as
possible, although when she finally crosses paths with him, she evades that she's avoiding
him.
On the way home from school, Il-sik suddenly comes to see Sun-oh in his class and immediately
hits him.
He apparently already knows that Sun-oh kissed his girlfriend because someone secretly took
a photo of the two of them while kissing.
Knowing that his best friend is being beaten badly, Hye-yeong rushes to help Sun-oh and
breaks up their fight.
After thanking Hye-yeong for helping him, Sun-oh again asks his best friend about his
feelings for Jo-jo, and Hye-yeong's answer is still the same.
Meanwhile, elsewhere, Jo-jo meets Duk-gu, who looks frustrated and heartbroken because
Gool-mi rejected his love.
He then hands Jo-jo a new cell phone, which he plans to give to Gool-mi, and asks her
to throw it away if she doesn't want it.
However, Jo-jo decides to take it and finds that the Love Alarm app has been installed
on the phone.
Jo-jo finds out that Sun-oh fought with her boyfriend, then goes to Il-sik to apologize
to him.
However, after realizing that the Love Alarm app doesn't sound when Il-sik is nearby, Jo-jo
finally finds out that he didn't like her all this time, and their love affair ends.
The next day, the students at school were shocked by the photo of Sun-oh and Jo-jo kissing
that circulated on social media.
Knowing this, Gool-mi becomes irritated and curses Jo-jo in front of their schoolmates.
Because Gool-mi brings up her family, Jo-jo becomes furious, and the two end up fighting
each other.
Not only insulted by Gool-mi, who humiliates her in public but Jo-jo is shunned by her
best friend, Jang-go, who is angry with her for thinking that she has wasted Il-sik's
love and attention.
But then, Sun-oh runs up to Jojo in her class and takes her away.
They went to the school gym, where each turned on the Love Alarm app to find out how each
other was feeling.
Sun-oh looks happy when his Love Alarm goes off, indicating that Jo-jo likes him.
On the other hand, Hye-yeong, who was there, chose to leave after discovering that Jo-jo
had sounded the Sun-oh's Love Alarm.
Hye-yeong, who also likes Jo-jo, chooses to give up the one he loves to his best friend
because previously, they had agreed to let Jo-jo choose with Love Alarm.
With all her troubles, Jo-jo spends more time with Sun-oh, who cares so much for her.
Since he hadn't had time to show his Love Alarm at the school gym, Sun-oh asked Jo-jo
to show him her Love Alarm when they were alone on the bridge.
Knowing that they both love each other through the Love Alarm application, Jo-jo and Sun-oh
finally decide to date.
They do not hide their love affair and always appear affectionate in public so that all
students know they are dating.
Meanwhile, Hye-yeong, knowing that Jo-jo has activated her Love Alarm, always avoids her
because he doesn't want her to know that he likes her.
However, this is disastrous for him, as Hye-young falls off his bike while trying to prevent
Jo-jo from sounding her Love Alarm.
While treating his wound in the school medical room, Hye-yeong is surprised by the presence
of Jo-jo, who looks surprised because her Love Alarm rings even though Sun-oh is not
nearby.
Since then, Jo-jo had always felt awkward when Hye-yeong was around her because she
had no idea that he actually liked her.
One day, Jo-jo is called by her homeroom teacher, who gives her a special card, in which she
will get free lunch in the school cafeteria if she shows the card to the canteen staff.
Jo-jo thinks her aunt paid for her school lunch, but Gool-mi reveals that Sun-oh paid
for it.
Gool-mi then spreads bad rumors about Jo-jo, now considered a materialistic girl by her
schoolmates, for taking advantage of Sun-oh.
Gool-mi did this because she was annoyed after Sun-oh rejected her declaration of love.
In fact, she intends to spread bad rumors about him.
However, Jo-jo, who knows about it, then asks Gool-mi to cancel her intention.
She tells Gool-mi to just hurt herself and never hurt Sun-oh.
While fighting, Gool-mi's mother arrived and defended her daughter.
Gool-mi's mother tells Jo-jo to leave if she always feels oppressed while staying at her
house.
Hearing that, Jo-jo finally left with tears in her eyes, lamenting the misery in her life.
When Jo-jo doesn't know where else to go, she meets Sun-oh, who smiles very sweetly
at her, which can take away the sadness in her heart.
He then invites her to dinner at a closed diner, where they have a heart-to-heart conversation.
Knowing that their school will soon be holding a study tour to Jeju Island, Sun-oh then invites
Jo-jo to go there together.
At first, Jo-jo had no intention of leaving.
But because Sun-oh asked her, she finally decided to take a study tour to Jeju Island,
even though until now, she is still shunned by her friends, including her best friend,
Jang-go, who is still angry with her for betraying Il-sik.
Jo-jo finally finds out that Jang-go has been in love with Il-sik for a long time when her
schoolmates get together to play their Love Alarm.
She then asks Jang-go why she hides her love.
However, Jang-go brings up Jo-jo, who kissed Sun-oh when she was still Il-sik's girlfriend.
Jo-jo, who feels very sad and frustrated that Jang-go now hates her, cries until she finally
falls asleep.
Jo-jo wakes up when her schoolmates scream in a panic because there has been a fire.
Seeing the fire blazing in front of her, Jo-jo thought back to the fire that killed her parents,
which triggered the trauma, so she rushed to the window and tried to open it like she
had before.
However, the teachers and her schoolmates saw Jo-jo's behavior and thought she was in
a trance and was behaving strangely.
Jo-jo looks frustrated, then runs off to meet Sun-oh.
Seeing Jo-jo crying in fear and hugging him tightly, Sun-oh takes her for a walk so she
can calm down, where they tell each other about each other's parents and spend the night
by the sea until morning.
The next day, on their way back to the hotel on a motorbike, Sun-oh and Jo-jo get into
an accident that leaves them unconscious.
Before losing consciousness, Jo-jo was reminded of her past, where it turns out that her parents
had planned the fire because they wanted to end their lives together.
The younger Jo-jo didn't understand when her parents chose to end their lives.
However, what made her suffer all this time was her parents had prepared her to die with
them too.
That's why, Jo-jo feels that meeting Sun-oh is a dream because, for the first time in
her life, she experiences what it feels like to be loved by someone with all his heart.
Four years later, the Love Alarm app has been updated, and Jo-jo is now working as an employee
at a wedding organizer company.
One day, Jo-jo sees Sun-oh across the street and then checks her Love Alarm, which is still
ringing.
However, Hye-yeong is also there, so she isn't sure which of them still likes her.
Jo-jo sees Sun-oh meet a woman named Yuk-jo, who immediately hugs him when they meet, making
Jo-jo assume that Yuk-jo is Sun-oh's girlfriend.
Her reunion with Sun-oh reminds Jo-jo of the accident they both had four years ago, where
he suddenly disappeared after the incident.
Even he never went to school again after that.
Turning to the present, Jo-jo draws illustrations and tells a narration about Love Alarm and
life to fill her spare time.
She then uploads it to social media using a pseudonym to hide her identity.
One day, Hye-yeong, who was doing his morning jogging routine, was surprised by the screams
of people who found corpses lying in the meadow not far from them.
The shocking incident became a trending topic on social media and a hot conversation in
the broader community.
After that, Hye-yeong, who received information about Jo-jo, who worked at a wedding organizer
company, tried to find her whereabouts because they had not seen each other for four years.
Hye-yeong finally reunites with Jo-jo, and although their meeting was quite short, he
looks pleased to be reunited with the one he likes.
Seeing Hye-yeong, who seems very neat, like he's been on a date with a woman, Sun-oh then
asks who is the lucky woman he is dating.
However, Hye-yeong says he's not dating any woman and tells him that he just met Jo-jo.
He tells Sun-oh that he still likes her.
Hearing this, Sun-oh felt angry because he thought back to Jo-jo, who had dumped him
in the past.
The next day, Jo-jo, who had just come out of the library, was startled by the Love Alarm
sound indicating that someone liked her within a ten-meter radius.
That person is none other than Sun-oh, who came to see her and asked her to stay away
from Hye-yeong because he didn't want her to hurt Hye-yeong as she had done to him a
few years ago.
It turns out that Jo-jo, who at that time came to Sun-oh's house and found out about
Sun-oh's family, decided to end her love affair with him because she thought that their love
affair would only hurt Sun-oh in the end.
Jo-jo activates a shield in her Love Alarm application so that the person she likes will
not receive notifications from her Love Alarm.
Turning to the present, the Love Alarm application will release the latest version, which is
predicted to detect someone's love feelings more accurately, and of course, with some
of the latest features.
The company that sponsors the Love Alarm application will hold an event ahead of releasing the
latest version of the Love Alarm application, where they will only invite certain people.
Such as Sun-oh, a well-known professional model, and Jo-jo, the owner of the Love Alarm
illustration account that has many followers on social media.
As time passes, Jo-jo and Hye-yeong become closer because he often helps her when she
is in trouble.
Jo-jo, who feels bad for Hye-yeong for not being able to repay his kindness, then asks
him not to expect too much from her because she won't sound anyone's Love Alarm after
her love affair with Sun-oh ends.
However, Hye-yeong doesn't seem to care about that as he tells Jo-jo that he still likes
her no matter what.
He proves it by sounding Jo-jo's Love Alarm which indicates that he still really likes
her even though they've been apart for a long time.
However, Sun-oh, who came to see Jo-jo later, also proves that he still likes her by sounding
her Love Alarm.
Sun-oh, sure that Jo-jo still likes him, hopes to rekindle his love affair with her.
But Jo-jo, who doesn't want to hurt him with their love affair, tells him that she wants
to try to like Hye-yeong as much as she likes Sun-oh.
Hearing this, Sun-oh became very upset and challenged her to sound Hye-yeong's Love Alarm
in front of him, and that's when he was about to give up her for Hye-yeong.
Long story short, the day for the release of the latest version of the Love Alarm application
has finally arrived.
Although the release was well received by most of South Korea's population, a group
of people opposed the release, even asking them to stop the Love Alarm application because
it had caused many fatalities.
Sun-oh comes there with Yuk-jo, as does Jo-jo, who gets an official invitation.
Hye-yeong, who knew Jo-jo had come, rushed off to meet her.
After the event, Jo-jo met Sun-oh, who was with his girlfriend.
Jo-jo's Love Alarm goes off because Sun-oh is nearby.
However, not long after, her Love Alarm sounded again because Hye-yeong finally arrived and
was within a ten-meter radius of Jo-jo.
At the same time, Love Alarm's developer released the latest version of Love Alarm, where the
application can detect who loves someone, not just liking or admiring.
Jo-jo, in the middle of two young men who like her, can now only wait to prove which
of Sun-oh and Hye-yeong loves her after the release of the latest version of the Love
Alarm application.
The moral that can be learned from this movie is actually everyone's feelings are unpredictable,
and these feelings can change over time.
A genuine love relationship requires more than feeling like each other because a love
relationship requires trust and good communication.