Metal detectors likely won't cause problems for people with pacemakers. But the Transportation Security Administration asks that people with a pacemaker, defibrillator, or other internal medical device not go through the metal detector. Instead, ask for a pat down or to go through the imaging-technology scan.
The American Heart Association suggests avoiding machines with powerful magnets, like MRIs. Some MP3-player headphones shouldn't be kept near a pacemaker either.