Bluetooth

Bluetooth is a technology that lets two devices communicate over short distances via radio. Instead of a cable, they send their data through the air as radio waves. For typical devices, the range is usually around ten meters. Common examples include wireless headphones, a computer mouse, or a smartwatch on your wrist. For the connection to work, both devices have to register with each other once. This process is called coupling or pairing, after which they automatically recognize each other again. Incidentally, the name comes from a Danish king from the 10th century, Harald Bluetooth, who united feuding tribes.

Why almost every device has Bluetooth today

About 25 years ago, every accessory had its own plug. Headphones, mice, keyboards, and printers each needed a matching cable. Bluetooth created a common standard that all manufacturers adhere to. That’s why headphones from any brand work with a phone from a different brand.

A second reason is low power consumption. Since 2010, there has been an energy-efficient variant called Bluetooth Low Energy, or BLE for short. A fitness band or a bicycle sensor can run for months on a small button-cell battery with it. This was the prerequisite for tiny devices to be networked at all.

Economically, the standard is a billion-dollar market. Several billion chips with Bluetooth are shipped every year. When manufacturers like Apple remove the headphone jack from smartphones, that shifts the entire accessories market. That’s why reports about new Bluetooth versions are also business news.

Radio channels, hopping, and the pairing thing

Bluetooth transmits in the so-called 2.4-gigahertz band. This frequency range may be used worldwide without a license. However, WiFi, microwaves, and many radio remote controls are also active there. So it fills up quickly and becomes prone to interference.

A trick called frequency hopping helps against this. The devices switch the exact radio channel up to 1,600 times per second, following a pattern known to both. If a channel is currently disrupted, that affects only a tiny fraction of the transmission. You can imagine it like a conversation in a loud room, where two people constantly change position together.

During pairing, the devices exchange a secret key once. This encrypts the subsequent connection so that strangers can’t simply eavesdrop. A common misconception is that Bluetooth is automatically insecure. Security vulnerabilities have indeed occurred repeatedly, but they were usually closed through software updates. It remains important not to leave pairing mode permanently open.

From car radios to the Corona-Warn-App

In everyday life, Bluetooth is mostly encountered with audio. Wireless earbuds, speakers, and car radios connect to the phone via it. Game console controllers, keyboards, and wireless printers also use the standard. Newer devices advertise Bluetooth LE Audio, which uses less power while offering better sound quality.

Bluetooth works less visibly in proximity detection. Small trackers like AirTags report their location via the phones of other people nearby. During the pandemic, the Corona-Warn-App used Bluetooth to measure how close two phones came to each other. In stores, transmitters called beacons detect whether a customer is standing in front of a particular shelf.

It’s important to distinguish Bluetooth from similar technologies. WiFi has greater range and speed but uses significantly more power and is mainly used for internet access. NFC only works over a few centimeters and is used in contactless payment. Bluetooth occupies the gap in between: a few meters, low power, direct connection between two devices.