Almost everything that uses electricity emits electromagnetic fields (EMF), and so does the Earth itself. The list of sources ranges from high-voltage power lines and cell towers down to the hair dryer you hold six inches from your head each morning. Understanding which sources produce stronger fields, and how quickly those fields weaken with distance, helps put everyday exposures in perspective.
Natural Sources
The planet you’re standing on is itself a giant EMF source. Deep inside the Earth, convecting molten iron in the liquid outer core acts as a massive moving electric current, generating the geomagnetic field. This is the field that lets a compass needle point north and, more critically, shields the atmosphere from the solar wind, a constant stream of charged particles blasted outward by the sun. The Earth’s static magnetic field measures roughly 250 to 650 milligauss at the surface, depending on your latitude.
Lightning is another powerful natural emitter. Each bolt sends out a burst of electromagnetic energy across a wide range of frequencies. Collectively, the roughly 2,000 thunderstorms happening around the globe at any given moment energize the Schumann resonances, a set of extremely low-frequency waves that pulse through the gap between the Earth’s surface and the upper atmosphere at about 7.83 Hz and its harmonics. The sun itself radiates electromagnetic energy across the entire spectrum, from radio waves to visible light to ultraviolet and beyond.
Household Appliances
Inside your home, any device with a motor, heating element, or transformer creates a magnetic field while it runs. What surprises most people is which appliances produce the strongest fields and how dramatically those fields drop with distance. The U.S. Environmental Protection Agency measured a range of common devices, and the pattern is consistent: fields are high at close range and fall off sharply within a few feet.
Hair dryers are among the strongest emitters you’ll hold near your body. At six inches, the median reading is about 300 milligauss (mG), with some models reaching 700 mG. Move to one foot away and the median drops to around 70 mG. By two feet, it’s roughly 10 mG, and at four feet the field is essentially indistinguishable from background levels.
Microwave ovens produce a median of about 200 mG at six inches, falling to around 40 mG at one foot and 10 mG at two feet. Unlike many appliances, microwaves can still register a detectable field at four feet, typically around 10 mG. Vacuum cleaners follow a similar profile to hair dryers: a median of 300 mG at six inches, dropping to 60 mG at one foot and 10 mG at two feet. Other notable household emitters include electric stoves, fluorescent lights, televisions, washing machines, and refrigerators, all of which follow the same steep drop-off with distance.
Power Lines and Transformers
High-voltage transmission lines are the most visible large-scale EMF source in most neighborhoods. Under a 380-kilovolt overhead line, magnetic field strength measured one meter above ground level reaches about 4.8 microteslas (roughly 48 mG). Underground cables of the same voltage produce slightly less, around 3.5 microteslas at ground level. These readings fall well below international limits, which in Europe are set at 100 microteslas for alternating-current installations.
The fields from transmission lines weaken considerably as you move laterally. By the time you’re 50 to 100 meters from the line, readings typically approach normal background levels. Neighborhood distribution transformers (the green boxes or pole-mounted cylinders) also produce localized magnetic fields, but because they operate at much lower voltages, their fields are generally only elevated within a few feet of the unit itself.
Wireless Devices and Cell Towers
Wireless technology emits radiofrequency (RF) electromagnetic fields rather than the low-frequency magnetic fields that appliances produce. These operate in the microwave portion of the spectrum, roughly 300 MHz to 300 GHz. The most common sources in daily life are cell phones, Wi-Fi routers, Bluetooth devices, and cellular base stations.
A typical Wi-Fi router operates at either 2.4 GHz or 5 GHz. At 20 centimeters (about 8 inches), a router running at a standard output power of 0.1 watts produces a peak power density of roughly 330 milliwatts per square meter. At one meter, that drops to about 13 milliwatts per square meter. For context, international guidelines set the exposure limit at 10,000 milliwatts per square meter for frequencies in this range, so typical Wi-Fi exposure is a small fraction of the limit.
Cell phones are actually a more significant personal RF source than routers or cell towers, simply because you press them against your head. A mobile phone can transmit at up to 3 watts, while most Wi-Fi routers operate at 0.25 watts or less. Cell towers, despite their higher total output, expose people at ground level to very low power densities because of the distance involved. Bluetooth devices emit at power levels roughly 100 times lower than a cell phone.
Smart Meters and Home Electronics
Smart utility meters, the digital meters that wirelessly report your electricity or gas usage, emit RF energy in brief bursts throughout the day. Their typical transmit power is 0.25 watts or less, compared to up to 3.0 watts for a cell phone. Field measurements taken directly on contact with a smart meter’s exterior registered 50 to 140 microwatts per square centimeter, while the FCC’s maximum permissible public exposure limit is 610 microwatts per square centimeter. A cell phone tested at the same time registered 490 microwatts per square centimeter. Because smart meters are mounted on exterior walls and transmit only intermittently, actual exposure inside the home is far lower than what you’d get from holding a phone to your ear.
Other home electronics that emit RF fields include baby monitors, cordless phones, smart speakers, gaming consoles with wireless controllers, and any device connected to Wi-Fi or Bluetooth. Wired electronics like lamps, chargers, and power strips emit low-frequency magnetic fields, but only at very close range.
Industrial and Medical Sources
Some of the strongest artificial EMF sources exist in professional settings. MRI machines use powerful static magnetic fields, commonly 1.5 or 3.0 Tesla, to image the inside of the body. For reference, 1.5 Tesla is about 15,000 times stronger than the Earth’s magnetic field. These fields are carefully contained within shielded rooms, but MRI suites require strict safety protocols because of the field strength involved.
Industrial induction heaters, used to melt or shape metal, generate intense alternating magnetic fields to heat conductive materials without direct contact. Arc welding equipment also produces strong localized EMF. Workers in these environments face higher occupational exposures than the general public, which is why workplace EMF limits are set separately from public limits.
How Distance Changes Everything
The single most important factor in EMF exposure is distance from the source. Magnetic fields from appliances and power lines follow an inverse relationship with distance, dropping off rapidly as you move away. A hair dryer that reads 300 mG at six inches reads just 1 mG at four feet. A Wi-Fi router that produces 330 milliwatts per square meter at 8 inches produces 13 milliwatts per square meter at about 3 feet.
This is why the appliance you hold closest to your body, like a phone or hair dryer, often contributes more to your personal exposure than a cell tower down the street or a power line across the road. The International Agency for Research on Cancer classifies radiofrequency electromagnetic fields as “possibly carcinogenic to humans,” a category that reflects limited evidence rather than a confirmed risk. It’s the same category that includes pickled vegetables and talc-based body powder. For most people, the practical takeaway is straightforward: distance is the simplest way to reduce exposure from any EMF source.