Most fitness trackers sit politely on your wrist, but Pavlok doesn’t play nice. You might call it Fitbit’s evil twin or the bad cop to the Apple Watch good cop.The wearable technology provides a small electric shock that its creators say can help curb smoking, eating doughnuts and watching too much TV. “Earn rewards when you succeed. Pay the price when you fail,” said a promo video for the device.

“There’s a real power in using a little bit of pain to help you break your bad habits,” the creator Maneesh Sethi said on ABC’s Good Morning America when the wristband was first released in 2014. Sethi appeared on the business-pitch reality show Shark Tank in 2016 but declined an offer from Kevin O’Leary. The second edition of the Pavlok bracelet was released in 2017 and is regularly priced at US$300. They’re for sale on Amazon for less.

Users can zap themselves with the wristband or grant a friend access through a smartphone app to administer the shock remotely when caught in the act. The zap strength is no more than 450 volts, according to the product website and is not enough to harm the user. Sethi said the shock, at worst, feels like the type of static shock that comes from rubbing your socks on the carpet and touching a doorknob. Still, according to some videos on social media, the shock can be pretty alarming.

A slew of testimonials on the Pavlok site claim that the bracelet has been effective. The creator has said it works in under five days. A Pavlok “coach” claimed one user became a “hyper-productive CEO” thanks to his device. Various users claimed it helped them stop eating sugar, biting their nails and hitting the “snooze” button.

“I would take a sugary item I would usually eat … and I would shock myself while eating it,” said one woman, claiming that after three weeks she had stopped eating refined sugar. “I feel like I’m back in control of my relationship with food.”

“I shock myself every time I bite my nails,” said another woman. “Now I’m very aware and I catch myself before I do it.”

The name Pavlok is a portmanteau of “shock” and “Pavlov,” a reference to Russian physiologist Ivan Pavlov who studied conditioned responses using dogs. The basic science behind the device is called “aversion therapy” and dictates that repeated use of unpleasant stimulus like an electric shock in conjunction with a certain behaviour will encourage the brain to form a negative connection to the behaviour. The Pavlok website cites 21 different studies on aversion therapy for behaviours such as smoking, weight loss, scratching and chronic cough. The site also claims to be undergoing its own research into the effectiveness of the device.

A writer for the New York Times health blog Well posted a positive experience with the device in 2016, but it doesn’t work for everyone. In 2016, a writer for The Verge tried to use a Pavlok on her nail-biting habit. It seemed to work at first, she wrote, and her nails even grew and stopped hurting. “But at the end of week one, I resumed biting my nails more fiercely than ever and I did something I found extremely liberating: I ignored the Pavlok on my wrist,” she wrote. The device didn’t recognize when she was biting her nails, so she eventually chose simply not to shock herself.

The newer versions of the Pavlok claims to know when its user has their hand near their mouth to bite their nails or when their chest hits the floor in an aborted push-up.