What things interfere with pacemakers and implantable defibrillators?

Noisemakers: Anything that creates electrical noise in the environment- strong magnetic fields, security scanners, cell phones directly over the device, cautery used to stop bleeding during surgery, magnetic fields caused by large motors, rarely microwaves. Most of these things can be avoided easily, if surgery is needed problems can be avoided with proper planning and device adjustment if necessary.

It Varies: Sources of electronic or magnetic fields (emi) can cause inappropriate function of a pacemaker or icd. Examples of these are mris, strong electric motors, or even security systems. Radiation (like for cancer therapy) can also damage or interfere with pacemakers/icds.

High Energy Sources: Induction cooktops arc welders, esp 240v and/or >200a alternators and other high-current generators nerve stimulators microwaves, phones, etc are safe. On manufacturers advice, any radio transmitting or receiving device is supposed to be ~6+ inches from the device but i've yet to see a cellphone interfere with a modern device.

Not much: Common household appliances and cellular phones are generally safe to use near an implantable defibrillator. It is best to avoid sources of significant electric current. For example, you should keep your icd 2 feet from an arc welder. You should not lean over your car engine while it is running. It is best to also keep large magnets off your device as well since this can affect its performance.

Not many: Arc welding is the main one.