NEW YORK (CBSNewYork) — There’s a new warning for anyone who wears a fitness tracker after some dangerous side effects have been reported.

Instead of promoting good health, some have led to a fitness fail.

New York Local News From CBS 2

Chris Nelson is an active dad who liked counting his steps and tracking his heart rate with his fitness tracker, but says while putting his three-year-old daughter Emily to bed his Fitbit Charge 2 shocked him.

The jolt caused him to drop his baby.

“It was clearly an electric shock,” he told CBS2.

Emily wasn’t hurt, but Chris says it left a painful lump on his wrist and caused his hand to go temporarily numb.

“The best I can figure, I was just shocked by the connector that was on my wrist,” the young dad said.

Mom Lauren Reiss swears two different Fitbit models shocked her.

“It shot up my arm, it was intense,” she said. “As soon as I looked down at my arm I noticed immediately that it hurt.”

She says one of the jolts left a lasting mark.

“You can see my burn,” she said. “It matches perfectly.”

If you search federal complaints you’ll find other claims against Fitbit. One complaint says “it sent a shooting, painful electric shock down to my fingers and up to my elbow.”

Another says the burning sensation lasted a couple of days. Reiss says it’s a danger that needs to be addressed.

Fitbit says it takes “all reports of potential issues seriously” and its products are “designed to prevent electrical contact with the user.” In each reported case it’s investigated, Fitbit says “the devices and batteries were found to be fully intact and functional, with no signs of overheating, voltage irregularities, or malfunctioning of any kind.”

The did suggest “it is more likely that the shock was caused by static electricity built up on the person.”

Kelly Robinson is a professional engineer who says static can build up on a body, but adds it’s often a scapegoat when companies can’t figure out what’s going on.

“I just don’t think it’s static,” she said. “I think there is something else going on.”

The reports of shocks concern consumer attorney Stuart Talley.

“If you had a pacemaker, if you were driving a car, something like that could cause a really serious injury,” he said.

Reiss does have a pacemaker, and now wears her Fitbit farther from her heart on her ankle instead of her arm.

Fitbit also sent Nelson a new, more advanced model. He says since then he hasn’t felt any jolts.

If you’ve ever experienced a shock from your Fitbit, you should contact them right away.