Remember when we all had to turn our cellphones off when planes took off and landed? How about turning them off around medical equipment? It turns out that when we look for something radiating out of cellphones that might harm us, we might consider magnetism.
While the Environmental Work Group was busy touting concerns, which we believe are unfounded, regarding cellphone radiation, another group of researchers was reporting on a “Big Fear, Little Risks”  – the magnetic forces emitted by our phones when they interact with implanted pacemakers and defibrillators.
A bit of background
Both pacemakers and defibrillators are small devices that provide an electrical jolt to the heart. For pacemakers, the jolts are meant to increase the heart rate when they sense they are too low and can cause dizziness and other problems. For defibrillators, the jolts are meant to jump-start the heart when it stops. In some instances, often related to surgery, it is necessary to turn these devices off. Rather than try and remove them, there is a “magnet mode” when exposure to a sufficient magnetic force will disable them.
A simple doughnut magnet, of approximately 90 gauss strength is the stand for triggering the magnet mode feature.
In the past, magnets of that strength were big and bulky, but today they are small enough to be found in our headphones, e-cigarettes, and cellphones. The latest Apple watches and iPhones feature a magnet with the strength to trigger magnet mode. 
Magnetic forces, like the problematic but not, radioactive energy of cell phones, diminishes with distance. The researchers set out to determine how far the magnetic field of those two Apple devices extended to better inform patients of the risk of inadvertently triggering magnet mode. Measurements were made using a gauss meter which, as you would expect, measures the magnetic field.
A short confession – I was able, as an undergraduate, to understand mechanical physics, but magnetism was a whole different problem. I couldn’t visualize the “forces,” What they meant by the right-hand rule still mystifies me. That said, what I do know is that magnetic forces radiate out in all directions, although unequally. If you are, like me, magnetism ill-informed, I do not believe our “knowledge gaps” will interfere with understanding this study.
The researchers measured the magnetic fields of these devices and found a maximum 1mm from the phone or watch case. At 21 mm (a little over ¾ of an inch), the magnet field was no longer strong enough to trigger magnet mode for a pacemaker or defibrillator. You will be happy to know that in the case of these devices, the FDA got the science “right.” They recommend that consumer devices that “create magnetic interference” be kept 6 inches away from your pacemaker or defibrillator.
The take-home message. Keep your phone and watch out of your shirt pocket.
 A shameless plug for our new movie, Big Fears, Little Risks
 The magnet, part of the MagSafe feature, allows wireless, physically secure charging between the devices and a charger.
Source: Static Magnetic field measurements of smart phones and watches and applicability to triggering magnet modes in implantable pacemakers and implantable cardioverter-defibrillators Journal of Heart Rhythm DOI: 10.1016/j.hrthm.2021.06.1203