The risk of insulting your partner isn’t the only reason you should reconsider giving them workout gear for Christmas.

Social media has made it abundantly clear that gifting your partner a $3,000 Peloton bike is a serious faux pas for potentially sending the wrong message, but one woman is revealing yet another peril of gifting your lover exercise accessories.

Jane Slater, a correspondent with the NFL, shared her cautionary tale on Twitter amid the Peloton commercial backlash. In a response to her NFL colleague Albert Breer, who tweeted yesterday that his wife was “not offended” by the Peloton he purchased for her years ago, Slater said she “loved” the FitBit her former boyfriend once gave her.

But the gift backfired in a big way. According to 39-year-old Slater, she and her ex would motivate each other’s workouts by mutually tracking their activity meters. Then she noticed an unusual bump in his heart rate — oddly, in the middle of the night.

“An Ex Boyfriend once got me a Fitbit for Christmas. I loved it. We synched [sic] 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,” wrote Slater in a tweet, which now has over 87,000 likes.

In a follow-up tweet, she clarified her story: “Spoiler alert: he was not enrolled in an OrangeTheory class at 4am.”

Her followers offered their support for Slater’s dismal cheating story, sharing their own similar tales of affairs outed by FitBit.

“Jane! My ex husband got caught in an affair because he was wearing the training watch and heartbeat monitor my mom bought him for Christmas – while ‘running’,” Twitter user @carey_gibbons wrote. “It was the under-one-minute heart rate spike that confirmed things for me! #prematuresayswhat”