Mobile Fundamentals · Wi-Fi & Bluetooth · Lesson 2 of 4

Bluetooth Basics

Pairing, range and the low-energy beacons all around you.

Short range, always on

Bluetooth is a short-range radio that links your phone to nearby gadgets such as earbuds, smartwatches, car stereos and keyboards. It uses the same 2.4 GHz radio band as many Wi-Fi networks.

The first time two devices connect, they pair. Pairing is a one-time introduction where the devices swap secret keys, so later connections are encrypted and happen on their own. That's why your earbuds reconnect as soon as you open the case.

Range depends on the hardware. Bluetooth radios come in power classes, and most phones are Class 2, which works out to about 10 meters (33 feet). Walls, metal and human bodies soak up the signal, so music can stutter when your phone is in a back pocket across the room. Devices with stronger radios can reach much farther in open air.

Short range gives you a little protection, since an attacker has to be fairly close. Being close is easy on a train or in a cafe, though. Keep your phone updated, because Bluetooth bugs do get found and patched, and say no to pairing requests you didn't start.

The low-energy kind

Classic Bluetooth is built for steady streams of data, like music going to your earbuds. That keeps the radio busy and uses a fair amount of battery. Bluetooth 4.0, released in 2010, added a second mode called Bluetooth Low Energy, or BLE. It's designed for small devices that only send a little data now and then.

A BLE device sleeps almost all the time and wakes for a few milliseconds to send a short message. Simple sensors and item trackers can run for months, sometimes years, on a coin-sized battery. Fitness bands, heart-rate straps, smart locks and smartwatches all rely on it too.

Many BLE devices also send out advertisements, tiny broadcasts that tell anything nearby the device is there. Item trackers use them so phones passing by can report where a lost bag is. The same broadcasts could be used to follow a person, so modern phones and trackers change their Bluetooth addresses regularly. iPhones and Android phones can also alert you if an unknown tracker seems to be traveling with you.