How Much EMF Does a Smartwatch Emit? We Published Our Test Report

Search for a low-EMF smartwatch and you will find pages selling shielding cases, protective stickers and pendants, most of them written to make you anxious enough to buy one. What you will struggle to find is a number.

That is strange, because the numbers are public. Every device sold in the United States with a radio in it has an FCC ID, and behind that ID sits a lab report measuring exactly how much it transmits. Nobody publishes theirs. So here is ours, here is a competitor’s for comparison, and here is how to pull up any watch you are considering.

The short answer

The Tribe Watch transmits at a maximum of 0.91 milliwatts. The FCC limit for the rule it is certified under is 1,000 milliwatts. So it uses 0.09% of what it is legally allowed — a margin of about 30 dB, or roughly one eleven-hundredth of the cap.

What that number actually measures

Conducted output power is what the radio chip produces before it reaches the antenna, measured in milliwatts or in dBm. It is the figure the FCC requires and the one you can compare between devices, provided both are measured the same way.

dBm is a logarithmic scale, which trips people up. Every 10 dB is a factor of ten. So 0 dBm is 1 milliwatt, 10 dBm is 10 milliwatts, and 20 dBm is 100 milliwatts. Our −0.43 dBm sits just below one milliwatt.

It is also a worst case rather than a typical one. FCC testing runs the device at a duty cycle of 98% or higher — transmitting almost without pause. A Bluetooth tracker on a wrist sends short bursts and stays silent between them, so the figure on the certificate is a ceiling the watch does not sustain in ordinary use. The same is true of every device in this article, which is what makes comparing certificates fair.

Worth being clear about what this is not: it is not a SAR figure. SAR measures how much energy your tissue absorbs, in watts per kilogram, and it is a different test. Our filing does not contain one, so we are not going to quote one — not even an estimate. If you see a wearable brand quoting SAR, ask which report it came from.

Tribe vs Fitbit vs Apple Watch

Here is the comparison most people actually want. It lines up the strongest transmitter in each device — because that, not the average of its radios, is what sets the upper bound on what the thing on your wrist can put out.

Read the last row carefully, because the two numbers in it are not the same kind of number. Fitbit’s 10.3 mW is measured — it comes off their own FCC form, on the same rule part and in the same frequency band as ours, with the form stating "output power listed is conducted" exactly as ours does. That is a genuine like-for-like, and the 11× gap is real.

Apple’s 200 mW is a class ceiling, not a measurement. It is the maximum an LTE radio of that power class is permitted to reach, and cellular radios throttle down sharply when signal is good, so an Apple Watch in a city is usually transmitting far below it. We have not yet pulled Apple’s own filing for the measured figure. When we do, this row gets updated.

What is not in doubt is that the LTE radio exists and ours does not. The 221× is a comparison of ceilings on radios of different kinds — accurate, and worth exactly as much as that description suggests.

The number that matters more: how many radios

Output power per radio is the figure everyone reaches for. It is not the important one. What determines how much a watch transmits over a day is how many transmitters it contains and how often each one is talking.

Here the gap stops being a matter of decibels and becomes a matter of hardware.

A cellular watch carries an LTE modem, and LTE user equipment in the ordinary power class is specified to transmit at up to 23 dBm — 200 milliwatts. That is a ceiling rather than a constant; cellular radios throttle down hard when signal is good. But it is a ceiling roughly 220 times ours, on a radio we do not fit.

That is the whole argument, and it is the same one we make about where your health data gets processed. A setting can be changed, a default can be reset by an update, a policy can be rewritten by whoever owns the company next. Absent hardware stays absent.

The trade-off is real and you should know it before buying: no cellular means the Tribe Watch cannot make calls or work away from your phone. If you want a watch that works without your phone, buy the cellular one — you are buying a cellular radio, and it will transmit like one.

How to look up any watch yourself

Five minutes, free, and it works for every device in your house. This is the part of the article we would most like you to use on us.

1. 1Find the FCC ID. It is printed on the caseback, in the manual, or in the device settings — on an Apple Watch, Settings › General › Regulatory. It looks like `2ASAU-S90`: a grantee code, then a product code.
2. 2Go to the FCC Equipment Authorization Search at `fcc.gov/oet/ea/fccid`. Put the first three or five characters in Grantee Code and the rest in Product Code.
3. 3Open the grant. In the results, click through to the grant or the Form 731. Ignore the test reports at first — the grant is one page and has what you need.
4. 4Read the Equipment Specifications table. Each line is one radio: lower frequency, upper frequency, and power output in watts. Multiply by 1,000 for milliwatts.
5. 5Count the lines. This is the part most people skip and it tells you the most. One line means one radio. Several lines, or a “composite device” flag, means more transmitters than the headline figure covers.

One honest caveat about the exercise: manufacturers can request confidentiality for parts of a filing, so some exhibits are withheld. The grant itself — frequencies and output power — is public in every case we have looked at, including ours.

What we are not going to tell you

We are not going to tell you that EMF from a wearable is harming you, because we do not know that and neither does anyone selling you a shielding sticker.

The radio in a smartwatch emits non-ionising radiation — it does not carry enough energy per photon to break chemical bonds, which is the mechanism that makes X-rays and ultraviolet light a known hazard. International exposure guidelines are built around tissue heating, and the power levels in this article are far below the point where measurable heating occurs. Harm below those limits is not established.

What we will say is this: wanting less of something is a legitimate preference and does not require proof of harm. People choose lower-alcohol drinks, quieter appliances and fewer ingredients without being asked to produce a study first. If you would rather have one small radio on your wrist than five, that is a reasonable thing to want, and you are entitled to the numbers that let you choose. Most of this industry would rather sell you the anxiety and the antidote at once.

How we handle it

The Tribe Watch has one radio because it only ever needs to do one thing: hand your readings to your phone over a short-range link. There is no cellular modem because it is not a phone. There is no Wi-Fi because your readings are interpreted on your own device rather than uploaded to us for analysis.

That is the same decision producing both results. Fewer radios is what you get when nothing needs to leave your wrist — which is also why there is no server-side copy of your health data to breach, sell or hand over, and why there is no subscription holding your own history hostage.

We are not going to claim our sensors read your body more accurately than anyone else’s, here or anywhere. They do not. The difference is what the device does with what it measures, and how much it has to shout to do it.

So: 0.91 milliwatts, 0.09% of the limit, one radio, and a report number you can pull up yourself. If a company will not give you the equivalent for the watch you are looking at, that silence is information too.