Taking to Twitter on December 5, Jane Slater shared details about her apparently unfaithful partner with her 121,000 followers.
"An ex-boyfriend once got me a Fitbit for Christmas. I loved it," she wrote.
"We synched up, motivated each other... didn’t hate it until he was unaccounted for at 4am and his physical activity levels were spiking on the app... Wish the story wasn’t real," she tweeted.
Having access to her partner’s movements meant Slater was able to catch him out when she realised a sudden spike in energy levels.
Some Twitter users pointed out she was accusing her ex of cheating when his heart rate could have been up due to a gym class.
"Spoiler alert: he was not enrolled in an OrangeTheory class at 4am," she confirmed.
"Had a guy get drunk and bring another girl home forgetting I was spending the night there," she said.
"We were set to go to church the next morning and I stayed in to get sleep.
"I could write a book."
This article originally appeared on 7NEWS