Wall Warts are the trade term for those little black bumps that stick out of our electrical sockets all over the house (1). We use them for all kinds of devices: charging cell phones, running laptops and most of the accessories we have come to rely on. As we migrate further into the digital age, our reliance on these innocuous power sources has exploded.
Traditionally, the appliances we had around the house, such as a stereo or TV, were constructed inside a metal frame that was electrically attached to a ground wire and three prong plug. This grounded metal frame provided quite a lot of shielding from electromagnetic radiation. We still see this in high power electrical appliances such as refrigerators, where this metal shielding additionally provides an essential safety feature enabling the appliance circuit breaker to trip if there is an electrical problem. That is why removing the third prong from a plug sidesteps the primary mechanism the device has to prevent the possibility of it electrocuting you. Now that most smaller appliances and accessories of modern living are housed in plastic cases, we rarely see the three prong plug, and there consequently there is an absence of metal electromagnetic shielding.
The reason that it is useful to have some awareness of wall warts is that the devices they power are almost without exception digital (2). When these are on, and many even when they are off, emit electromagnetic radiation which can potentially be harmful. The absence of the ground plane excludes the ability for these devices to have any form of shielding and their ground reference can float quite far from the ground reference we are connected to on the earth (3). The amount of radiation these devices emit is a minuscule fraction of the radiation cell phones and Wi-Fi emit, but they are a radiation source. We may only use a cell phone a few minutes a day, but can be exposed to these small radiation sources 24 hours a day.
There is not much we can do about this as we rely on many of these devices sometimes on an hourly basis. One thing we can do is if we have a choice between a desktop and laptop PC, work on the desktop. It is worth not keeping any of these wall wart, two wire or battery operated digital devices near where you sleep. Unplugging these devices when not used saves energy and eliminates them as a source of radiation.
I can envision a future where people will look back on this time in regards to electromagnetic radiation as we look back on the dark ages in relation to medicine and religion. I am sure we will continue to use digital equipment, but predict that it will be heavily shielded with a proper ground reference. We may even have some sort of monitoring mechanism as is currently used in dealing with radioactive elements with a maximum permissible safe lifetime exposure to electromagnetic radiation.