MP3 player headphones can cause potentially dangerous interactions with pacemakers and implantable defibrillators. For safe use, the headphones must be at least 1.2 inches (3 cm) from the implanted devices. Unrelated research did not find adverse reactions to pacemakers and defibrillators from iPods, Bluetooth headsets, iPhones, electric blankets, hand-held airport metal detectors or pills swallowed to perform video endoscopy.