Bluetooth LE

When you stream music to wireless earbuds, the sound cannot cut out, so your phone and earbuds must exchange massive amounts of data nonstop. This is like leaving a phone call open around the clock—no matter how large the battery is, it will rarely last more than a few days.

Fitness trackers, however, do not need to transmit your step count, body temperature, or heart rate hundreds of times a second. Sending that data once every few seconds—or only when you open the companion app—works just fine. Bluetooth LE was engineered specifically around how these Internet of Things (IoT) gadgets actually operate.

The core secret of this technology is spending almost all of its time in an ultra-low-power sleep mode. Whenever there is fresh information to report, it wakes up in a millisecond, tosses over a tiny packet of data, and plunges right back into a deep sleep.

Even though they share the Bluetooth name, classic Bluetooth and Bluetooth LE are essentially two distinct technologies tailored for different purposes. If classic Bluetooth is a heavy cargo truck hauling continuous audio and large files, Bluetooth LE is a nimble bicycle delivering a brief memo and heading right home. (With the arrival of LE Audio in Bluetooth 5.2, this line has started to blur, but their architectural foundations remain separate.)

Classic Bluetooth burns power continuously just to keep an active connection open between paired devices. Bluetooth LE can also pair and maintain a connection when needed—like with a smart band or a smart door lock—but it can also broadcast brief status signals into the air without establishing an active pairing at all.

Because of this streamlined design, connecting and transmitting data takes a fraction of the time. While its transfer speeds and payload sizes are smaller than classic Bluetooth, power consumption can drop anywhere from half to as little as one-hundredth depending on the use case.

To look a bit closer, Bluetooth LE eliminates power waste by drastically simplifying its connection handshakes and frequency channels. Out of all available radio channels, it uses just three dedicated channels to broadcast advertising packets that essentially shout, "Here I am!"

This simple setup is why lost-item trackers and smart tags can run for a year or more on a single coin-cell battery. The tracker only emits an occasional faint chirp. Passing smartphones pick up this signal in the background and forward its location to the cloud.

Today, Bluetooth LE serves as an indispensable foundation for countless smart devices where swapping batteries is a hassle—from retail beacons pushing promotional alerts as you enter a store to smart scales, continuous glucose monitors, and keyless entry door locks.