Bluetooth Low Energy (BLE) Basics: How It Works and Your First BLE Scan

Bluetooth is used in many devices around us, from smartwatches and fitness trackers to wireless sensors and smart home products. It lets devices exchange information without cables.

But not every Bluetooth device needs to send data continuously. A pair of headphones needs a steady stream of audio, while a temperature sensor might only need to report a small reading every few seconds or minutes.

For devices that send small amounts of data, saving power is often a priority. That is one reason Bluetooth Low Energy (BLE) is so useful.

In this guide, we'll look at what BLE is, how it saves energy, how devices find and connect to each other, and how to try a simple BLE scan yourself.

1. What is a communication protocol?

Before getting into BLE, it helps to understand communication protocols.

Think of two people trying to talk without knowing the same language. They might hear each other, but they cannot easily exchange information. Electronic devices have a similar problem.

A communication protocol is a set of rules that tells devices how to exchange data. These rules can define how devices identify each other, connect, send information, and handle errors.

Wi-Fi, Ethernet, and Bluetooth all use standardized protocols. Bluetooth is particularly useful for short-range wireless communication between nearby devices.

2. What is Bluetooth Low Energy?

Bluetooth Low Energy, also called BLE or Bluetooth LE, is a wireless technology designed to exchange information while using relatively little power.

BLE was introduced with Bluetooth 4.0 in 2010. It is especially helpful for devices powered by small batteries, such as wearables and sensors.

Imagine a battery-powered temperature sensor. It may take measurements regularly, but it does not need to keep its radio active all day. It can send information during short periods and spend much of the remaining time in a low-power state.

BLE operates in the 2.4 GHz ISM band and is common in embedded systems and Internet of Things (IoT) projects.

Bluetooth Classic and BLE: what's different?

Bluetooth Classic (BR/EDR) has traditionally been used for uses such as wireless audio. BLE was designed to make short, efficient wireless exchanges practical for low-power devices.

Modern BLE can also be used for audio through LE Audio. So it is not correct to say that Classic is only for audio and BLE is only for sensors. They are different Bluetooth technologies with different designs.

3. How does BLE use less power?

Wireless radios consume energy when sending and receiving data. BLE reduces unnecessary radio activity in several ways.

Short communication events

Instead of keeping the radio busy all the time, a BLE device can wake up, communicate briefly, and return to a low-power state.

Advertising without connecting

A BLE device can send small messages called advertising packets. Nearby scanners can receive these packets without making a connection first.

Adjustable intervals

Developers can choose advertising and connection intervals that fit the application. A sensor that sends occasional measurements may use longer intervals than a device that needs quick updates.

Small data exchanges

BLE provides a practical way to exchange compact pieces of information, such as sensor values or device status.

Important: BLE does not guarantee long battery life on its own. Real power use also depends on the hardware, software, radio settings, and how frequently the application communicates.

4. Advertising and scanning explained

Two of the first terms you will meet when learning BLE are advertising and scanning.

Advertising

A BLE advertiser sends packets to announce that it is nearby. Depending on the device, the packets may contain a device name, service identifiers, manufacturer data, or other application information.

For example, a BLE beacon may broadcast an identifier that another device can recognize.

Scanning

A scanner listens for those advertising packets and reports the devices it discovers.

A scan might show information like this:

These are illustrative readings, not results from a real scan.

RSSI means Received Signal Strength Indicator. It measures the strength of the received radio signal, usually in dBm. A value closer to zero generally means a stronger signal, but walls, interference, and antenna position can affect the result. RSSI is not an exact measurement of distance.

BLE has 40 radio-frequency channels. Three channels—37, 38, and 39—are the primary advertising channels. The other 37 channels are used for data communication and can also support certain extended advertising procedures.

5. How do BLE connections work?

Scanning helps a device find nearby advertisers. Some applications can use the advertising information alone. Others need to create a connection to exchange more data.

For a typical BLE connection, there are two roles:

• Central: Usually a phone, computer, or gateway that starts the connection.
• Peripheral: Usually a sensor or another device that advertises and accepts a connection.

For example, a heart rate monitor advertises itself. A phone scans, finds the monitor, and connects. After that, the two devices can exchange information according to the features they support.

These connection roles are different from the GATT client and GATT server roles covered next.

6. GAP and GATT in simple terms

You will often see GAP and GATT in BLE documentation. They do different jobs.

GAP: Generic Access Profile

GAP covers important rules and procedures for device discovery and connections, including advertising and scanning.

An easy way to remember it:

GAP helps devices find and connect to each other.

GATT: Generic Attribute Profile

GATT defines how data is organized and accessed using services and characteristics.

For example, an environmental sensor could expose a service with characteristics for temperature, humidity, and measurement settings.

Characteristics may support operations such as:

• Read: Get a value from a device.
• Write: Send a value to a device.
• Notify: Receive updates from a device without repeatedly asking for them.
• Indicate: Receive an update that requires confirmation at the GATT protocol level.

A GATT server provides the attributes. A GATT client can access them according to the device's permissions.

7. A quick look at the BLE protocol stack

BLE works through several layers and protocols. You do not need to memorize all of them to get started, but knowing their purpose can help when reading documentation.

In most projects, a Bluetooth chip, firmware, and software stack already take care of the lower-level details. Developers can focus on what their applications need to do.

8. Where is BLE used?

BLE appears in many kinds of products:

• Wearables and healthcare: Fitness trackers, heart rate monitors, and connected sensors.
• Smart homes: Smart locks, temperature sensors, lighting controls, and automation products.
• Industrial monitoring: Sensors that report equipment condition or status.
• Environmental monitoring: Devices that measure air quality, CO₂, temperature, and humidity.

Each application has different needs, but all can benefit from efficient wireless communication over short distances.

9. Try a BLE scan yourself

Reading about advertising and scanning is useful. Seeing the results on your own computer makes these ideas easier to understand.

There are several tools for experimenting with BLE. One option is BleuIO, a Bluetooth Low Energy USB dongle that supports simple AT commands for BLE operations.

BleuIO can be used for scanning, advertising, and supported BLE connections. It also has a browser-based Web App that lets you send commands to a compatible dongle from a supported browser.

Scan for nearby BLE devices

Connect your BleuIO dongle to your computer, open the BleuIO Web App, and connect to the dongle.

Then enter:

AT+CENTRAL
AT+GAPSCAN=5

Here's what the commands do:

1. AT+CENTRAL sets the dongle to the central role.
2. AT+GAPSCAN=5 scans for nearby BLE devices for five seconds.

A scan response may look like this:

AT+GAPSCAN=5
SCANNING...
[01] Device: [1]30:63:C5:D0:B1:DE RSSI: -38
[02] Device: [0]D0:76:50:80:0A:98 RSSI: -75
[03] Device: [1]27:5D:B8:2E:96:B0 RSSI: -51
SCAN COMPLETE

This is sample output for illustration. Your actual results will depend on nearby devices and the dongle's configuration.

The scan demonstrates a basic BLE concept: the scanner can discover advertisers without connecting to them.

What to explore next

After scanning, you can try exploring advertising data, connecting to a compatible BLE peripheral, and working with GATT services and characteristics.

BleuIO has tutorials and project examples using tools and platforms such as Python, JavaScript, Raspberry Pi, STM32, and Arduino.

You can explore the BleuIO AT command documentation and find more examples on the BleuIO website.

10. Final thoughts

Bluetooth Low Energy makes wireless communication practical for many battery-powered and connected devices. Understanding advertising, scanning, connections, and GATT gives you a good starting point for learning how BLE works.

You do not need to build a complete Bluetooth application for your first experiment. Start by scanning for nearby devices, look at their advertising information, and build from there.

Sometimes a simple scan is enough to show just how many BLE devices are active around us.