Should you worry about the EMF from your smartwatch?

A Bluetooth fitness band transmits at a few milliwatts, roughly fifty to a hundred times less than the phone in your pocket, and it sits within the limits the FCC sets for wrist worn devices. The question worth asking is not whether the watch is powerful, it is whether yours has a cellular radio and whether you keep it on for the eight hours you are asleep.

What a wearable is actually transmitting

Most fitness trackers and most watches, most of the time, are doing one small job. They collect steps and heart rate and hand that data to your phone over Bluetooth Low Energy.

The chips that do this are genuinely tiny. Common wearable Bluetooth radios transmit in the range of 3 to 6 dBm, which works out to about 2 to 4 milliwatts. A standard LTE handset is allowed up to 23 dBm, or roughly 200 milliwatts, and it reaches for that ceiling whenever signal is weak.

So the band on your wrist and the phone in your pocket are not the same order of magnitude. They are not close.

What the science says, plainly

Wrist worn devices are tested and regulated. In the United States the FCC sets a limb exposure limit of 4.0 watts per kilogram averaged over 10 grams of tissue, a separate and higher threshold than the 1.6 watts per kilogram over 1 gram that applies to a phone held against the head. The ICNIRP, the international body much of this guidance draws from, sets its own comparable limits.

Published values for cellular smartwatches land well under that limb ceiling. Recent Apple Watch models with cellular report figures in the region of 0.83 to 0.86 watts per kilogram, which is about a fifth of the limit they are measured against.

We will not pretend the file is closed. In 2011 the IARC, the cancer research arm of the World Health Organization, classified radiofrequency electromagnetic fields as a Group 2B possible human carcinogen, meaning evidence worth studying rather than proof of harm, and the NTP 2018 studies from the US National Toxicology Program found some evidence of tumors in rats exposed to RF well above ordinary phone use. Neither studied wrist worn Bluetooth devices.

The one spec that actually changes the answer

A Bluetooth only tracker and a cellular smartwatch are different devices wearing the same shape.

A cellular watch has a real mobile radio in it, on the same bands and reaching for the same power levels as a phone, because it has to talk to a tower rather than to something three feet away. When it is untethered from your phone and holding a cellular connection on its own, it is closer to a small phone strapped to your wrist than to a step counter.

If you do not know which yours is, check whether you paid for a data plan for it. That is the whole test.

The trade-off is the opposite of a phone

A phone is high power and usually at some distance. Pocket, desk, counter. A wearable inverts both terms. The power is very low, and the distance is zero, permanently.

This is why we keep coming back to the same three principles. Distance is doing nothing for you here, because the device is strapped to skin. Source strength is small, which is the good news. That leaves time, and time is the only one of the three you still control.

For a watch you wear from breakfast to bedtime, that is a reasonable trade-off, and we are not going to tell you otherwise. It is the other eight hours that are worth a thought.

The night question

Sleep tracking is the reason most people keep a watch on around the clock, and it is a real benefit, so this is a genuine trade-off rather than an easy call.

Worth knowing: most wearables are not streaming all night. They log to internal memory and sync in bursts. But many people also leave the phone charging on the nightstand so the watch has something to sync with, and now there are two radios at the head of the bed instead of none.

If you want the sleep data, keep the watch and move the phone. If you were only wearing it overnight out of habit, taking it off is a free change and you lose nothing.

What a sticker can and cannot do here

BioHarmonize stickers are made for phones and personal devices, and a smartwatch is a personal device, so it is a reasonable place for one. What a sticker does not do is change a device's transmit power or its duty cycle, and we are not going to imply it does. The habits in this article are free, and they are the substance of it.

What to do this week

Find out whether your watch has a cellular plan. Two minutes, and it sorts you into one of two very different situations.

Then decide the night on purpose instead of by default. If you use sleep tracking, keep the watch on and move the phone off the nightstand. If you do not, take the watch off at night and charge it across the room.

That is it. No fear required, and nothing to buy.

Optimize your environment. Unlock your potential.

Yarden and Jessica