12Wi-Fi, Bluetooth and the free-for-all bands

The short version: Your router, earbuds, smart plugs and a growing number of city sensors all transmit without anyone holding a license. In the US that is allowed under the FCC's Part 15 rules, on three conditions: you get no right to any frequency, you must not cause harmful interference, and you must put up with whatever interference you receive. Much of this traffic shares the same few "ISM" bands with machines that were never meant to communicate at all, starting with the microwave oven in your kitchen.

What does "must accept any interference received" mean?

What you see: A line of small print on the label or in the manual of almost any wireless gadget.

That sentence is the deal behind Part 15, the section of US federal rules that lets ordinary people run low-power radios with no license. Under 47 CFR 15.5, the operator of a Part 15 device "shall not be deemed to have any vested or recognizable right to continued use of any given frequency."³⁴ Operation is allowed only on condition that "no harmful interference is caused," and the device must accept interference from licensed stations, from other unlicensed radios and from industrial, scientific and medical equipment.³⁴ If an FCC representative tells you your device is causing interference, you "shall be required to cease operating the device," and you may not switch it back on until the problem is fixed.³⁴

In practice that means nobody owns the channel your Wi-Fi is on. Your neighbor's router, a wireless camera down the hall and a phone hotspot on the bus are all equally entitled to it, and none of them can complain to the government that the others are in the way. Licensed users, such as a TV station or a cellular carrier, are in a different position: they paid for or were assigned protection, and Part 15 devices must stay out of their way.

Every rule here is federal. Massachusetts does not license or regulate unlicensed radio separately, so the rules in Boston are the same as in Boise.

What is an ISM band?

What you see: Nothing, but your Wi-Fi, Bluetooth and smart-home gear all cluster on a handful of the same frequencies.

An ISM band is a slice of spectrum set aside internationally for industrial, scientific and medical machines that use radio energy for something other than communication, such as heating. Unlicensed radios are allowed to share these bands as guests, and the rule for guests is blunt: "communications equipment operating in ISM bands must tolerate any interference generated by ISM applications."²⁰²

The International Telecommunication Union (ITU) splits the world into three regions, and not every ISM band exists everywhere:²⁰²

That regional split is why a US smart-home lock or LoRa sensor built for 915 MHz is the wrong product in Europe, which uses 863-870 MHz for the same jobs instead.²⁰³

The 2.4 GHz band became the home of consumer wireless after a 1985 FCC ruling opened it to unlicensed spread-spectrum radios.²⁰⁴

In the US, the spread-spectrum rule is 47 CFR 15.247. It lets frequency-hopping and digitally modulated radios operate in 902-928 MHz, 2400-2483.5 MHz and 5725-5850 MHz, with a maximum peak conducted output power of 1 watt for most systems and less for frequency-hoppers that use fewer channels.³⁵ Machines such as microwave ovens fall under a separate rule, Part 18, which lists ISM frequencies including 915 MHz (plus or minus 13 MHz), 2450 MHz (plus or minus 50 MHz) and 5800 MHz (plus or minus 75 MHz),³⁶ and gives ISM equipment on those frequencies "unlimited radiated energy" within the band.²⁰⁵

Where did Wi-Fi come from?

What you see: The fan-shaped Wi-Fi icon on every phone, laptop and coffee shop window.

Wi-Fi's family tree goes back to 1971, when ALOHAnet linked the Hawaiian Islands with UHF packet radio.²⁰⁴ The modern standard is IEEE 802.11. Its first version came out in 1997 and topped out at 2 Mbit/s; 802.11b followed in 1999 at 11 Mbit/s.²⁰⁴

The catchy name came from the branding firm Interbrand and was in use by 1999.²⁰⁴ The industry group that certifies devices started as the Wireless Ethernet Compatibility Alliance (WECA), began promoting standardized Wi-Fi in 1999, and is now the Wi-Fi Alliance.²⁰⁶ When it marked 25 years in 2024, the Alliance counted more than 21 billion Wi-Fi devices in use.²⁰⁶

What do Wi-Fi 4, 5, 6 and 7 mean?

What you see: A number on a router box, or a small "6" or "7" inside the Wi-Fi icon on some phones.

For two decades, Wi-Fi versions went by IEEE letter codes that meant little to buyers. In October 2018 the Wi-Fi Alliance switched to generation numbers.²⁰⁷

The numbering for Wi-Fi 1 through 6 comes from the Alliance's 2018 announcement.²⁰⁷ Wi-Fi 7 brings three headline changes: channels 320 MHz wide (available only in the 6 GHz band), Multi-Link Operation, which lets a device use more than one band at once, and 4K QAM, a denser way of packing bits onto the signal that the Alliance says is about 20% faster than the 1024 QAM used before.²¹⁰ At launch, the analyst firm IDC forecast 233 million Wi-Fi 7 devices would ship in 2024.²¹⁰ Whether you need it depends on whether your other devices and your internet connection can make use of the extra capacity.

Why does my router have 2.4, 5 and 6 GHz bands?

What you see: Two or three network names from one router, or a setting called "band steering."

Each band is a trade-off. Lower frequencies travel farther and pass through walls better; higher frequencies have more room for wide channels and fewer neighbors crowding in.

• 2.4 GHz is the worldwide ISM band.²⁰² It is the most crowded: Wi-Fi shares it with Bluetooth, Zigbee, Thread and microwave ovens.
• 5 GHz came with 802.11a.²⁰⁴ Its top end overlaps the 5.725-5.875 GHz ISM band.²⁰²
• 6 GHz is the newest. In April 2020 the FCC made 1,200 MHz of spectrum, 5.925-7.125 GHz, available for unlicensed use.²¹²

The 6 GHz band was not empty. Utilities, public safety agencies and network backhaul operators use fixed microwave links there, so the FCC set two tiers. Low-power indoor devices may use the whole band. Higher, "standard-power" devices may use 850 MHz of it only under Automated Frequency Coordination (AFC), a database service that tells an access point which channels are safe given the licensed links nearby.²¹²

In the US, 5 GHz Wi-Fi runs under the FCC's U-NII (Unlicensed National Information Infrastructure) rules, which cover 5.15-5.35 GHz and 5.47-5.895 GHz below the 6 GHz band.³⁷ Power limits are set separately for 5.15-5.25, 5.25-5.35, 5.47-5.725, 5.725-5.850 and 5.850-5.895 GHz.²¹³

Can I use 6 GHz Wi-Fi outside the US?

What you see: A router or phone that offers 6 GHz at home but not abroad, or fewer 6 GHz channels in Europe.

Countries split on how much of the band to open. As of December 2021, the US, Canada, Brazil, Saudi Arabia and South Korea had opened the full 1,200 MHz, along with several other Latin American countries. The EU, by Decision 2021/1067 in June 2021, opened only the lower 480 MHz (5945-6425 MHz), and Australia and New Zealand were consulting on the lower 500 MHz.²¹⁴

The UK already allows Wi-Fi in 5925-6425 MHz. In July 2026, Ofcom decided to allow AFC-controlled higher-power Wi-Fi across the upper band, 6425-7125 MHz, with regulations expected in autumn 2026, and on July 20, 2026 it opened a consultation proposing low-power and very-low-power Wi-Fi in 6425-6585 MHz.²¹⁵ Ofcom's documents also cover mobile use of the band, which is the other contender for that spectrum in Europe.²¹⁵

Japan's regulator, MIC, sets its own 6 GHz rules, so check its current position before relying on 6 GHz there.

Why is Bluetooth called Bluetooth?

What you see: The angular blue "B" icon, and your earbuds reconnecting the moment you open the case.

Bluetooth is a short-range radio in the 2.4 GHz band. Its Special Interest Group (SIG) formed in February 1998 with Ericsson, Nokia, IBM, Toshiba and Intel as founders.²¹⁶ The name honors Harald Blåtand, "Bluetooth" in English, a Danish king who reigned roughly 940-981 AD.²¹⁶

Classic Bluetooth hops pseudo-randomly among 79 channels in the 2.4 GHz band, which helps it dodge Wi-Fi and microwave ovens sharing the same air.²¹⁶ Bluetooth Low Energy (BLE), introduced with version 4.0 in December 2009 and once called "Wibree," uses 40 channels and is built for devices that run for months on a coin cell.²¹⁶ Bluetooth 5.0 in 2016 quadrupled range.²¹⁶

Because 2.4 GHz is an ISM band worldwide, Bluetooth works the same in Boston, London and Tokyo.²⁰²

What is a Bluetooth beacon?

What you see: A store app that pops up a coupon near a certain aisle, or a small plastic puck stuck high on a wall.

A beacon is a BLE transmitter that repeats an identifier over and over. Apple introduced its iBeacon format at WWDC in 2013. Each beacon broadcasts a UUID plus two numbers called Major and Minor, and an app that recognizes them can estimate whether the phone is Immediate, Near or Far.²¹⁷ Apple switched on iBeacons in its 254 US stores on December 6, 2013.²¹⁷

The beacon itself only announces; it does not receive. Any location inference happens in the phone, through apps that have been given permission to listen, and that is where privacy questions about beacons arise.

What are Zigbee, Z-Wave, Thread and Matter?

What you see: A logo on a smart bulb or door lock box, or an app asking you to "add a Thread border router."

Smart-home sensors usually skip Wi-Fi in favor of low-power mesh radios, where each mains-powered device relays messages for its neighbors so data can hop around walls to reach the hub.

Z-Wave came from the Danish company Zensys. Sigma Designs bought Zensys in 2008 and sold Z-Wave to Silicon Labs in 2018; the Z-Wave Alliance dates to 2005.²¹⁹ Because its frequency differs by region, a US Z-Wave lock will not talk to a European hub.

Thread comes from the Thread Group, formed in July 2014 by members including Nest Labs, Samsung, ARM, Silicon Labs, Qualcomm and Yale.²²⁰ It uses the same 802.15.4 radio as Zigbee but carries internet-style IPv6 addresses (via a compression layer called 6LoWPAN), and a border router connects the Thread mesh to your Wi-Fi or Ethernet.²²⁰

Matter is the shared language on top. Version 1.0 and its certification program launched October 4, 2022, from the Connectivity Standards Alliance, "formerly the Zigbee Alliance," whose members include Amazon, Apple, Comcast, Google, Samsung SmartThings and Signify.²²¹ Matter does not have its own radio: it runs over Ethernet, Wi-Fi or Thread, and uses BLE only to commission new devices.²²¹ The idea is that a Matter light switch works with any brand's app or speaker.

On "Zigbee or Z-Wave?": Z-Wave's sub-GHz signal avoids the crowded 2.4 GHz band, while Zigbee and Thread share 2.4 GHz with Wi-Fi but have the newer Matter ecosystem behind them.

What is LoRa, and how far does it reach?

What you see: A small white box with a stubby antenna on a parking meter, a farm fence or a water tank; or "LoRaWAN" on a sensor spec sheet.

LoRa trades speed for distance. It is a proprietary form of chirp spread spectrum co-developed by Cycleo and Semtech, sending about 0.3-27 kbit/s with a practical range around 10 km (6 miles).²²² Semtech's own figures are up to 4.8 km (3 miles) in a city and 16 km (10 miles) in the country.²²² That is enough for a soil-moisture reading or a "trash bin full" alert, not for a photo.

LoRaWAN is the networking protocol on top, and it has a plan for each region: US902-928 (US915) in the US, EU863-870 (EU868) in Europe, plus AU915-928, four AS923 variants, IN865-867, KR920-923, CN470-510 and EU433.²⁰³ Europe also limits how much of the time a device may transmit on 868 MHz (its duty cycle). CEPT's 2001 decision on non-specific short-range devices, ERC/DEC/(01)04, set 25 mW and under 1% of each hour in 868.0-868.6 MHz, under 0.1% in 868.7-869.2 MHz, and 500 mW and under 10% in 869.4-869.65 MHz.²²³ Later European rules have revised parts of this framework, so check the current national rules.

What is the Helium network, and is it legit?

What you see: A crypto-mining "hotspot" box in a friend's window, or ads for Helium Mobile.

Helium is a LoRaWAN network built by the public: people buy and plug in hotspots and earn tokens in return. The company began in 2013 and its network launched in 2017 under Amir Haleem, using LoRaWAN for devices and the HNT token for rewards.²²⁴ It moved to the Solana blockchain in April 2023 (a change known as HIP 70).²²⁴ Nova Labs launched Helium Mobile in 2023, a phone service using T-Mobile plus Helium hotspots, and in June 2026 announced its sale to Noble Mobile.²²⁴

The project has a disputed record. In July 2022, reports said Helium had listed Lime and Salesforce as partners without formal relationships; Haleem disputed this in December 2023.²²⁴ The SEC sued Nova Labs on January 17, 2025, alleging unregistered securities and misleading partnership claims. On April 10, 2025, the SEC dropped the securities claims, and Nova Labs agreed to a $200,000 settlement without admitting or denying the allegations.²²⁴ Readers can weigh that record for themselves; the radio side is standard LoRaWAN.

By the project's own count in a December 19, 2025 year-in-review post, Helium had more than 120,000 active hotspots across the US and Mexico, carried 15.72 petabytes of data in 2025 and logged more than 600,000 Helium Mobile sign-ups.²²⁵

Why does my Wi-Fi drop when the microwave is on?

What you see: A video call that stutters, or a speaker that cuts out, every time someone reheats coffee.

The microwave oven is "the most commonly encountered ISM device," and it runs at 2.45 GHz,²⁰² right in the middle of the band your 2.4 GHz Wi-Fi uses. A home oven pumps about 1,000 W into the food.²²⁶ The metal box and door screen hold almost all of it in, and US rules cap what may leak out at a tiny fraction of that power (the FDA limit is below).²²⁷ That small leak is still loud next to a Wi-Fi signal that has crossed two rooms.

The oven's energy overlaps 2.4 GHz Wi-Fi channels 7 through 11.²²⁶ In a March 2009 test, a running oven cut throughput by 21% on channel 1 and 51% on channel 9.²²⁶ Under the ISM bargain, Wi-Fi has no grounds for complaint: it is the guest.²⁰² Practical fixes follow from the numbers: move the router away from the kitchen, pick channel 1 for 2.4 GHz, or use the 5 or 6 GHz band, which the oven does not touch.

You may have heard that 2.45 GHz is the "resonant frequency of water." It is not: physicist Christopher Baird of West Texas A&M University writes that oven microwaves "are not tuned to a resonant frequency of water," and that the frequency is used largely because regulators allocated it to ovens.²²⁸

In the US, oven leakage is an FDA rule, not an FCC one. Under 21 CFR 1030.10, which applies to ovens made after October 6, 1971, leakage may not exceed 1 milliwatt per square centimeter at any point 5 cm or more from the oven's external surface before the oven is sold, and 5 milliwatts per square centimeter at any such point over the rest of its life.²²⁷ For questions about RF exposure and health, see health.

In Boston

Unlicensed radio is the same in Boston as anywhere else in the US, because the rules are federal.³⁴ Two local touches: the 902-928 MHz band that Boston-area LoRa sensors and smart meters use exists only in the Americas,²⁰² and MassDOT has used Bluetooth radios to time traffic on state highways (see everyday radios).

Elsewhere in the world

• UK and EU: The equivalent of Part 15 is called "licence-exempt" use, with a similar no-protection principle plus power and duty-cycle limits. Europe uses 433 MHz and 863-870 MHz where the US uses 902-928 MHz.²⁰²²⁰³
• Canada, Australia and Japan: ISED, ACMA and MIC each set their own license-exempt rules, with their own bands and power limits; check the national regulator before using imported gear.
• 6 GHz: The EU opened only 5945-6425 MHz; the UK is extending into the upper band in 2026.²¹⁴²¹⁵
• Smart home: Z-Wave moves to 868.42 MHz and sub-GHz Zigbee to 868 MHz in Europe; 2.4 GHz Zigbee, Thread and Matter are the same worldwide.²¹⁹²¹⁸

For how event crews share crowded spectrum at a show, see show wireless.

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