The literature documents a number of common sources of possible interference. Interference with MRI and electrocautery have been observed (1, 2). Outside the hospital, store security devices and personal digital assistants (PDAs) have been evaluated (3, 4). In 1997, Hayes et al published a randomized, prospective trial concluding that cellular telephones impacted the functioning of pacemakers, but that they did not seem to have any effect at any significant distance (5). They showed that a phone being used at the ear was sufficiently far away to prevent a health risk and recommended that phones not be put in shirt pockets or used near the device.