Headphone makers love to brag about the fancy magnets they use to drive their buds, but it turns out that hanging tiny focused magnetic fields around you neck can have unintended consequences -- a new study says that headphones can interfere with heart devices like pacemakers and defibrillators when held within an inch of the device. The interference can be be so disruptive that a defibrillator can fail to fire live-saving electric charges, so we'd say that anyone counting on technology to keep their ticker ticking should be extra-careful with where they stow their 'phones -- and although researchers didn't find any interference from cell phones, it probably can't hurt to keep those out of your shirt pockets as well.