How Does Bluetooth Low Energy Work?

1. Prepare to communicate

Before any radio exchange, a product’s firmware decides what it will do. A sensor might prepare a small value to broadcast, or expose a GATT service for a connected app to read. The choice determines whether another device only needs to listen or must establish a connection.

2. Advertise and scan

A connectable peripheral can announce its presence in advertising packets. A broadcaster can also send advertising data without accepting connections. A central or observer scans to receive those packets and decides whether the information is relevant. A scan may show a name, address, or signal strength, but the exact fields depend on the advertising device.

For example, an environmental monitor could place a measurement in an advertisement. A nearby scanner can use that measurement without opening a connection if the data is present and readable in the packet.

3. Connect only when needed

If the application needs data or controls that are not in the advertisement, a central may request a connection to a connectable peripheral. The devices then exchange packets at agreed connection events. Connection interval and latency affect responsiveness and power use. A connection may fail if the peripheral stops advertising, is out of range, is already connected to another central, or rejects the request.

4. Exchange data through GATT

Many connected BLE applications use GATT. A GATT server groups related data into services; characteristics represent values or controls. A GATT client can discover services, read permitted values, write where allowed, or subscribe to notifications. Properties and security permissions determine which operations actually succeed.

A thermometer might expose a temperature measurement characteristic. A client can subscribe to notifications only if that characteristic supports them. The exact identifiers and permissions come from the device’s documentation or discovery results.

5. Continue or close

After the required data exchange, the connection may close. The peripheral may resume advertising so another central can find it. A broadcast-only interaction has no connection to close: scanners simply continue listening or stop scanning.